General 318-340 questions

I will definitely keep that in mind I didn’t think about that. And will a b body rear work on an a body car?

Not really, the spring perches are wider as are the ends of the axles. Now you are in to custom offset wheels or figuring what will work. Do you know what brakes (10" drums?) and bolt circle (small bolt pattern 5 x 4.00?) you have now?