74 dart rear end in a 64 dart ,7 1/4 will it fit

i don't know, but why do you want a 7 1/4?

The best reason I can think of is that the buyer wanting a '74 7¼ is because he wants to change from a small bolt pattern rear axle to a big bolt pattern rear axle and NOT have to change the drive shaft. HOWEVER, the 7¼ has to come from a disk brake equipped '74 to have the BBP.

I just finished this swap on my 73 /6 car that I'm converting to disk brakes & BBP. Other than getting the danged u-bolts off, it was an easy swap. FWIW, Mopar put 7¼s on 273 HP cars with Torqueflite. I had one.