Thanks for the input.
Yes, M7 x 0.75 metric fine seemed to make sense (even though 'strange' given the age and history as pointed out).
However, I happed to have an M7 x .75 die but it wouldn't run through it - wouldn't even start on it. That's strange also, because it 'should' given the dimensions - maybe it's the thread form?
Even with a magnifying glass, I'm afraid I wasn't able to see whether it was 55 or 60 degrees.
Yes, I have 32TPI gauge and that wasn't right either.
I did a bit more Googling of thread conversons etc and one chart shows .747mm equals 34TPI. However, 34TPI is a very odd imperial thread for reasons beyond me, explained here -
www.practicalmachinist.com ("...if I had a 58T change gear on my chinese lathe (lead screw pitch 1.5mm) I could cut a 33.997 TPI thread, actually better than you can do on a lathe with an imperial leadscrew").
I guess I could just re-cut threads with in the eccentric with an M7 x .75mm tap?? (even though I would have to use a die to cut the shaft rather than turn it on the lathe).