Could of course be a different axle in the 'correct' cups.
Yeah, did consider that. The more I find out the more I think the axle at is a BB-7200.
That Sutherland pdf is great. So much information. Haven't had a chance to digest it but it appears that the 7500, 7300 and 7200 bottom brackets differ from all the other Shimano JIS/ISO BB's at that time.
They aren't interchangable with other models as the Axle is to thick at the cup. They also list JIS as the closest alternative
fit rather than ISO as with all the other older shimano ISO BB's. Which would suggest that these had a slightly larger taper than the ISO of the day. JIS being the largest and closest fit.
So initially it looks like during the late 70's early 80's Shimano had 3 different square taper standards. Shimano's original version of ISO, the newly introduced JIS and it appears a slightly oversized Square ISO taper on the 7500, 7300 and 7200 BB's.
I've read of people suggesting Campag ISO tapers with 7500 track cranks because they think Campag ISO tapers offer the closest fit. I'm sure I've even read this on Sheldon Brown's site. But from what I've just learnt it appears that JIS would be the closest alternative.
It's no wonder we all struggle to get perfect chainline with all these unknown factors.