Turns out I was approaching the problem from the wrong end. After consulting my array of vintage Capri manuals whilst partaking of a small sherry, it turns out that the spring clips in question were on the other end of the linkage rods. 
A few minutes later, after a bit of back and forth under the car then back into the cockpit, the linkage is out and discarded like the Cylon’s first attempt at creating an octopus. 
I then supported the gearbox on a jack, wedged a bit of wood between the sump and the front crossmember (to stop the engine tipping back), loosened off the bolts on the rear mount, unhooked the clutch, speedo and reverse cables, removed the bellhousing to engine bolts and attempted to wiggle the box free. It was still catching on something though, and it took me far too long to realize there was still a tiny bolt left to undo. All the ones I’d done were nice, big and obvious 17mm heads, but this was a 10mm headed one that seemed to serve no apparent function – other than buggering up my karma. 
Ah well, with a bit more wiggling and a gradual lowering of the jack, the box came free…
The oil round the inside front of the bellhousing all seems to be old gunky engine oil, rather than from the box, and appears to have soaked in thought the engine/bellhousing joint over the years. The inside of the bellhousing is dry beyond that first inch. Normal or abnormal? 
I’m now left with a gearbox sized hole in the gearbox tunnel. 
Today’s question, then, is do I get a full clutch kit or just a new release arm bearing? Benefit of replacing the clutch now would be that I’d have to take the box out again to do it later, but it’s showed no signs of slipping thus far, so seems a tad pre-emptive … plus I’m short of pocket money this week. 
I’m now thinking that pretty much all the stuff I’ve read about going from a 4-speed to a 5-speed seems to be based upon folks going from one version of the Type 9 box to another, as they all say that the box is two inches longer to account for the fifth gear assembly. The difference between a 4-speed Type H and a 5-speed Type 9 box, however, is much less …
The old box is 1cm shorter than the newer one. Now I’m wondering if I’ll actually need a shorter propshaft, so I’ll probably just wait and see. I’m also wondering if I’ll need to move the gearstick hole …
That’s it for today folks 
exboyracer: Those rod change boxes are wierd 
I would change the clutch release bearing as a minimum, it should be cheap enough hopefully!
The oil will be coming from the crankshaft rear oil seal.
It’s probably a good idea to replace it, but this will mean removing the clutch, flywheel and sump so it’s a bit of a mission, even if the part itself is cheap
I suppose it all depends on how much bothered you happen to have in stock
merp0: Trial fit the box Stu, that should answer most of your queries. Also check the input and output shafts have the same diameter and amount of splines.
And another thing, check the condition of the spigot bearing in the flywheel. I had one of those go and it’s a whole lot of trouble getting the box back out for a bearing that cost a few quid.
dangerousdave: Take the clutch cover off and look at the clutch stu to see how worn it is and if you need to change it wont take 5 minutes
And definately change the release bearing if the clutch is ok.
Otherwise you look like your coping very well with this task
me: Crankshaft rear oil seal can sing for its supper if it’s that much work to change it. I’m trying to only work on one “module” of the car at a time, to try and prevent the job creep that ends with half the car on the workbench – and for today’s purposes, the engine and gearbox are two different modules. 
Sounds like the spigot bearing is on the far side of the clutch. If the clutch comes off, it’d make sense to replace the bearing too, as I’ve heard tales of woe from folks who didn’t.
Would taking the cover off for a look-see mean I’d need one of those alignment tools to put it back on again? Is wear on a clutch plate obvious? Can you tell I’ve no idea what I’d be looking for?
olly22n: You will need an alignment tool, you won’t know its out of line until the car is back on the road and its too late!
The release bearing is attached to the clutch arm, it should just pull off, but to get these its £30 from burtons, and a new clutch is £50 with the bearing included…
Crankshaft seal imho is well left alone…
exboyracer: The initial clutch alignment is only important when the box is being refitted as if it is slightly out of line it will prevent the gearbox input shaft from mating with the splines on the friction plate. Once the car is in use, as the clutch cover engages and dis-engages the friction plate self-centralises.
I will admit, though, that a centraliser can make refitting the box a bit less of a hit-and-miss struggle
Graham: [on the old box being 1cm shorter than the newer one] thats bugger all really, if the spline is the same i’d just reuse the old prop
Graham: [on needing an alignment tool] not quite, if the clutch is out of alignment the box wont go back on the engine, if it goes on you have nothin to worry about,
for many years i used to align clutches by either feel or eye, if you install the clutch with the cover bolts just nipped you can usually center the plate by feeling the overlap between the center plate and cover plateat three points around the circumference of the thing,
or by eye, if you can get yourself so you can look straight at the center of the plate and into the crank spiggot, then when everything looks exactly lined up it usually is
then tighten the cover bolts,
or maybe take an angle grinder to the old gearbox and cut off the old input shaft, and use that as an alignment tool, you wont find a better one.
therealpinto: I have actually done the exact swap…
The prop length is OK but the splines are different 🙁
Gearstick hole does not have to move 🙂 (or should it be :-/ since you removed so much stuff?)
Hope that a 5-speed gearbox crossmember fits straight on, I don’t know since we didn’t get 5-speed Capris in Sweden.
As for the clutch kit…it’s easy to change later. For clutch alignmen anything with;
a) roughly the diameter if the pilot bearing first
b) then roughly the diameter of the clutch disc splines
will work. Be it plastic, steel, aluminium or wood 🙂
Oh, the reverse switch wires will be too short…
olly22n: you’ll need a 23 spline prop shaft
therealpinto: I was suspecting that the body mounts for the gearbox crossmember is different in 4 spd/5 spd shells…
I used some lengths of 20x20x3 mm aluminium box sections to make adapters for the 4 spd crossmember. You need to move the mount downwards and back about 20 mm. A nicer solution might be to cut and weld a cross member but my solution worked for almost 10 years before swapping to the T5 gearbox.