we have just started our first such conversion on a MRS. we will write up an article and put it on our web site in the next month or so. Interested parties can phone.
engine & box now sitting in donor shell. no particular problems with this but it is a very tight squeeze. we have modified the alloy end cover on the gearbox to get more chassis clearance but suspect some minor chassis mods will be needed in finished job, to give 'real-world" clearances. changing the front bank of spark plugs is impossible without either removing the engine or cutting an inspection hole in the rear body work, where the soft-top folds down.
custom mounts being made. at this stage we are keeping the MRS rubber mounts in all locations and changing the metal brackets
exhaust is under consideration. it looks like the easiest route is to use the headers designed for the SW20 conversion and notch the front crossmember to give sensible clearances around the flange.
wiring.. no particular problem but days of work
rear crossmember needs to be radically modified. prototype in progress.