It's over 50 years since I had a Mk1 Cooper S box but I remember that 2nd gear had 1 less tooth than others, giving less ratio gap 2nd to 3rd.
2nd gear was a ripper...!
Edit my bad it was 3rd gear different according to John Smidt's bible just found.
Had 1 tooth more I think.
@cooperess, A form gears had bushes in them and B form ones had loose rollers in them. 22G582 is A form
22G980 is B form.
A form was early, pre 64 I think.
I had put a mate's 63 Cooper box into my 850 in 1965 and that was B form.
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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.