I have a 73 Q code conv. and just spent the summer trying to get motor mount to work.
I have the clam shell type with the number 665 stamped on them. there is also one that has 663 stamped on them.
I first tried the open kind that is glued together two pieces of metal with rubber in the middle. they lasted 300 miles.
Next I went ot the Poly mounts.
There is a trick to making them bolt up. You have to loosen all the bolts on the frame mounts right to the last tread, start all bolt in the mount, let the weight of the engine down on the mounts and than tighten up all the bolts. I was told to also loosen the bolts on the poly mount so the poly can adjust itself inside of the mounts. I didn't do this but it looks like it may have been the right thing to do , because it pulled the poly a little inside the mount cage.
The company that makes them has it listed that they will fit a 73, check out there web site
Good Luck