There are many 'universal' motor mounts out there like this
. Also, you can make your own using factory rubber. IF the Ford had the big front X-member like a late model GM, you can get the mounts from a junk yard GM, bolt then to the engine, lower it into the bay and weld the mounts in place. Many ways to skin that critter.
Tranny and rear end depends on what you want to do with the car. If your aim is a daily cruiser, look at a 350, 200R4, or 7004R auto tranny. The latter two give you the economy of overdrive but are slight more complicated to get working properly. For a rear end, the ford 8" would be the best choice. You are correct the stock '51 rear cannot be used with open drive line components.