Phil,
There are a number of things you should know about fitting a 5 speed box ILO a 4 speed box. I am in the final stage of fitting one to my Sprint.
* You need a 5 speed clutch pressure plate, 8.5? clutch plate and release bearing.
* Perhaps a longer speedo cable ? although my 4 speed cable fitted perfectly.
* The gear lever position is 25mm (1?) further rearward and a modification designed by Victor Hollnagel is recommended.
* The exhaust ?Y? piece will not fit as it fouls the gearbox because it is has a bigger profile than the 4 speed. A new one that goes around the gearbox will need to be made. I may be able to help you there.
* You will probably have to make adjustments to the exhaust centre pipe to mate-up with the ?Y? piece.
* The gearbox mount position is 96mm further rearward and of the correct height ? so you don?t need spacers. This position can be addressed by modifying the 4 speed bracket. You will need to remove the support pieces, reverse it and drill new holes to suit the chassis.
* You need a specific 5 speed propshaft with four special propshaft bolts. (same as the diff bolts).
* The 5 speed box is 120mm shorter in length than the 4 speed and has a flange connection to the propshaft. You will need to check if the access hole in the +2 chassis/body is in the correct position to locate and assemble the gearbox/propshaft flanges. This was a problem with the Sprint so I had to do the John Clegg trick and cut a hole in the bottom of the chassis box section in order to fit the special propshaft bolts.
elan-f14/lotus-speed-gearbox-t19761.htmlI'm sure there must be some other things that I have not thought of off the top of my head, and if I do, will let you now.
You don't say where you're located, so other advice may not be suitable.