cant help, but assuming yours is 12v 845 cc (2 bolt) and most donor vehicles are gtl/1108 which wont fit (3 bolt fixing)
if you can hit it to make it work it would be worth find car electrician locally to fit new brushes cheaper than exchange/new starter
probably irrelavant, but many years found new starter in collection of spares i bought thought great a new 6v r4 starter just what i need only to discover it was for a dauphine and rotates opposite direction!!
pity yours is not a pre 1973 then you could of used the starting handle !!!