I had the same issue on the last BBC in my 69 Camaro... it was correct V's, wiring looked good, I had a heat shield, etc... would start cold... but when hot & could barely even get a "click"/ or movement when starting. Bought a new mini starter. Upon taking the old starter out, I found that the starter motor base was not tight to the mounting plate... you could wiggle it some... just a little... I tightened it & used some Blue Loctite & never had that issue again. Good luck!