Usually aftermarket motor mounts won't last - they are usually cheap Chinese parts that fail after a few moderate accelerations. The best solution I have found is to get the Poly-Loc replacements from Schumacher Creative Services, which can not break by design. The replacement for the 65 Chryslers I believe (from my catalog which is a few years old) would be C3EP. Call them to confirm fitment using original brackets (which the catalog states for your model and 383) and price. 206 364-7151
Schumacher Creative Services
I have learned the hard way not to compromise on motor mounts ever again. And only Schumacher seems to have the right stuff available off the shelf.
Mancini Racing also sells the Schumacher mount, so I would get it from either Schumacher or Mancini, whichever is cheaper including shipping.