Maybe I'm confused (likely) but I'm sure my 69 - made for 1970 a body a833 has the larger 727 slip yoke ?
and agreed the machine shop drilled holes and ground like crazy on my diaphragm clutch to get it to balance.
since then I've changed both flywheel and clutch and have noticed no difference. But next winter break I'll address all that and likely change clutch again. The op is talking street car with street tires? Wouldn't a diaphragm clutch be a better daily driver ?