folks,
now at the satge of rebuilding my mk1motor. have got the replacement mk1 caseS and all other bits and will do the mains and seals when i am in there.. and gaskets i need.(sprocket had sheared and came off and trashed previous case).
so my question is..does the whole mk2 box just slip in...or do i have to modify anything....much rather the mk2 box to avoid the centre nut and more security of the mk2...
thanks D

Mk2,3 and AR gearbox internals are exchangeable. Mk1 is not. I.e. None of the other gearbox internals will fit in Mk1 casings. There are two particular bits -

The water pump drive - this can be fixed by changing the bearing that sits in the casing as the diameter of the shaft is larger 2/3/AR.

Mismatch of clutch bearing housing and clutch shaft means there is no bearing that can match Mk1 casing and 2/3/AR shaft.

I got round it by using Mk1 shafts except for a Mk2/3/AR final drive shaft and swapping the gears. BUT I had to do some machining - viewtopic.php?f=14&t=3484&start=80 I had to got through every part of two gear boxes and ensure everything lined up with the correct spacing. Unfortunately you can't just change the final drive shaft as the gears just don't fit.

Much easier to swap with Mk2/3/AR cases!