OK..
3 synchro boxes in general are not as strong as the later 4 synchro ones. Yeah the Mk1 S had one but it wasn't real strong either, particularly 1st gear.
Whether it's got a puddin' stirrer or a remote, the strength of these boxes (apart from early 850's POS cone synchro one) is about the same.
4 synchro remote boxes are much better. Haven't personally busted one yet. If you fit the magic wand (puddin' stirrer) it is still a stronger box than any 3 synchro one..
A Mini Deluxe 3 synchro box will take a 1275, with a bit of grinding here and there. But as I said, the Mini K or Mk2 S box is better.
Forget about using the old 850 box. Just save the shifter and diff housing..
_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
