The trans mount looks correct for 64-66, rubber is cracking not sure if split through, you will have to check. rear leaf spring front location looks stock. Time for testing, install the thicker insulator & check for clearance and driveline angle. If pipe is hitting frame, you have a few choices use thinner insulators and modify trans mount down, modify header tube for clearance, my last option is insert shim between K frame and frame rails. I would not use sold mount if driving on street.
