Not So Fast.
I had two bits of luck when addressing the propshaft.
The first was that there was available off the shelf a Hardy Spicer type yoke conversion for the Ford T9 box. The second bit of luck was that the joints themselves were exactly the same size - 25 x 75mm - as the RME's.
With the mounts all tacked in place for a final check that everything was going to fit....
... and with an extra bit of anti-vibration matting squeezed in between the plates for luck, I turned my attention to the propshaft. I had to go back to YouTube to remind myself of the sequence for dismantling UJ's as it's been a while and I usually get in a complete muddle with one end of the UJ hung up and seemingly impossible to shift. But all was sweetness and light, the secret being to tap the yoke until the chosen cap is proud enough to grip in a vice. Despite being stored in the village pond for the last 50 years - as most vintage car spares seem to be - sure enough, each cap obliged, emerging tortoise-like from its shell.
Just out of interest, I began to dig a bit deeper on propshaft angles and speeds and this is where I realised that I'd been a bit hasty in making the engine mounts. 'Ignore the angles of dangle at your peril', intoned the various technical sites I visited.
I knew that I had to do something about the differential as it was pointing downwards on account of the duff springs. I removed those springs and replaced them with the set from an RMA. There's a few more leaves which would make the back end stiffer, but I'll cross that bridge in time. I had a couple of bits of 10mm brass which, located at the front of the axle brackets, acted as a wedge and gave me the magic 3°.
To get the 3° at the gearbox output shaft, I had to lift the front of the engine - which played havoc with the front and centre engine mounts. I took 10mm out of the centre mount, lowering the plate on which the bellhousing rubber blocks sit and added 7mm to the front of the forward engine mounts to get the engine and mount plates properly aligned. Good job they were only tacked together! There's a rebate in the actual engine casting that takes an aluminium block, separating the rubber mount from the engine. I had only one of these which is why there are two plates cut from scrap in the picture above. I'll go and raid Chumley's scrap box and replace them with a 20mm block on both sides. That should give me the 3° down at the gearbox end.
And for a bit of fun I thought I'd try and work out what the Morris/Ford/Riley combination would theoretically achieve if all went according to plan. 1st, 2nd and 3rd seem a bit short, but 4th and 5th look to be perfectly acceptable - 99mph at 5000rpm is quite fast enough.