Freaky Bottom Bracket

Ive been reconditioning my fathers old tourer recently. Sun GT10, its about 30y.o. steel frame. Lost the usual bits and pieces and replaced the old steel wheels with something a bit more modern.

The chainline could be better to be honest, so im condsidering replacing the cranks in the future.

Currently it has a square taper bottom bracket, with a stud extension that the cranks are attached with a nut (not a bolt, a nut?)
Thinking about replacing the BB, Ive measured it and the shell is 70mm. I consulted Sheldon and its quite possibly a 71mm Raleigh 26tpi cup. Are these available anywhere? did they have different axle lengths?

Alternatively does a JIS crank sit further inboard than ISO?

Any other suggestions?

http://www.monsterevo.co.uk/Non%20Car%20Pics/tumbleweed.jpg

Currently it has a square taper bottom bracket, with a stud extension that the cranks are attached with a nut (not a bolt, a nut?)

thats very very normal, half my bikes have BB's like that. works just the same as if there was a bolt.

Id expect your bottom bracket are completley standard B.S.A/I.S.O if it is a 30 year old British bike. (is sun british?)

just swap your BB into another bike to be sure.

the Miche Primato BB fits a standard 68mm BB -Shell.

If your BB -shell is 71mm that means when you fit it you will have 1.5mm spare on each side, as the cups of the Miche BB will just screw into it, given you have compatible threads.

Edit] Just had a look on sheldon] you might be outta luck cos the threads are different. You have measured the shell ? not the shell and the BB face also ?

Don't you measure from outside face to outside face then to get BB shell width?!?

.[URL="http://www.sheldonbrown.com/"][/URL]