318 Craigslist Special swapped into a 65 Wagon

I hate to throw this out since the engine is already in the car, but when you use a ~68+ engine with an earlier transmission you need to install a special ring over the snout of the torque converter so it fits in the larger crank bore. Search FABO for more info. If it isn't vibrating when you rev it, you probably don't have a problem to fix. If the torque converter bolts stay tight, should stay OK and balanced.

I didn't quite follow the motor mount issue (did look at your photos). I understand that 273 and 318 blocks appear identical on the outside, other than the casting letters. The 360 is the only small block that has different motor mount attachments , and on only one side.