Suspension and Brake swap?

The 63-66 centerlinks were narrower. The later style wont fit, plain and simple. The rest of the steering linkage must remain stock for the 64. All manual gearboxes were basically the same, so retaining the manual setup should be no problem. In fact, besides the gearbox the ONLY parts that are the same are the lower control arms, so you can re-use your old ones no problem. The only 73 parts you will need to use are the spindles, lower pall joints, upper ball joints and upper control arms. You will also need the 73 master cylinder and associated plumbing. If you 73 rear end is a 7 1/4 you can just swap the axle shafts and brakes, saving the hassle of loosening a couple dozen rusty bolts.

Making your own motor mounts? To each their own, but why reinvent the wheel? These are factory parts, and not particularly rare. Get them off the same parts car you score the oddball 64-66 exhaust manifolds, throttle linkage, radiator, center link, and 90 degree oil filter off of. Or Schumacher makes new ones.