The age of the car puts this as having a 4 speed Rover box, not a Moss. The Rover 5 speed (LT-77) was introduced later in the year this car was produced. Moss boxes were only used up until around 1972 or '73...
You'll find an R380 very notchy and slow to change compared to the 4 speed Rover. Also the chassis (and body) is narrower than the later +8 which was fitted with the R380. I expect you would need major alterations to the transmission tunnel, chassis cross member etc. and that is assuming it will fit. I also expect the prop shaft will need shortening.
If you just want taller gearing, it might be worth investigating a change to differential internals to raise the gearing a bit...
Cheers,
There's a fair chance that your 1975/6 Morgan was fitted with a 5 Speed type chassis and the wider body. Not many people know this and trot out the usual stuff published in books and magazines. Why do I know? Because I have owned mine since 1981 and it was on its original chassis and I did exactly the same conversion.
The 5 Speed type chassis was I believe introduced during 1975. Early (pre-1975) 4 speed chassis are identified by the curve in the chassis cross-member under the bellhousing; 5 Speed chassis have a straight U sectioned cross-member. The only difference between a 1975/6 4 Speed chassis and a 5 Speed on is that the rear gearbox mounting plate location is slightly different. It's an easy job to remove and re-weld the mounting plate for its new location.
You'll need a shortened propshaft, converted bellhousing (Morgan did mine many years ago), different slave cylinder, different handbrake mounting, recalibrated speedomter and new cable (Speedy Cables), and potentially a new gearbox cover. If obtaining a suitably modified bellhousing proves difficult you could go for a concentric clutch; the bellhousing will still need the housing for the clutch actuating arm to be removed and plated; I suspect that John Eales or Mulfab (Peter Mulberry) will be able to assist.
If you want dimensions and measurements, I have them.
