Morris Minor Owners Club

Yes -when I ran Viva 12" wheels on my Autocross Mini (before anyone else used 12" wheels I may add!) - I made up special wheel nuts which fitted the 3/8" studs - and fitted into the gap - and also fitted the larger taper section on the Viva wheels!
To get back to the Q - if the studs are closer together - then they are v likely to be Marina/Triumph pitch - which is 3 3/4" PCD. The calipers I think will be Ford with that 'type 16' on them.

was under the car today so here's a pic of the marina setup & mounting for comparison.
Also noticed the back of the stub axle on yours looks different, has it had that changed to accommodate the hubs?

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well i can tell you they are not midget/sprite discs
sorry this is my only contribution