Can anyone suggest a suitable oil for a Midget/morris axle?....I would assume its going to be similar to that of the English axle etc...?

I read the 750 Formula forum quite regularly and see no sign of you being blacklisted for fitting a bike engine into an ex 750 formula car....unless I'm missing reading a vital thread!? - I've met a lot of them and they're a bit eccentric perhaps (aren't we all!) but I can't see them having a problem with what you're doing unless you were planning to run the car in a 750 Formula race - ie cheat ..... otherwise Britishtrident is probably your only hope on here!

If memory serves me true these axles originally used EP90 gear oil.
It is 35 years since I owned one though !!

Yes, definately EP90.