Help with converting b body 8 3/4 to A body 8 3/4 for my 1964 plymouth Valiant

Hello guys

Thanks for all the help you have been giving me on my build

So i ordered the doctor diff axles which are for a 52 5/8s flange to flange

My question is. All the info i can find is that the 66 and up a body is 52 5/8s flange to flange. Does this apply for my 64 or does it need to be smaller ?

The machine shop is saying that this is the spec for 62 and up. A body 8 3/4 see foto attached

Does this mean i should return the 52 5/8s axles and get 51.4 axles ?