I have a tired and weak 312 motor in by 57 Bird. A "Ford Guy" near me has a 1956 Merc 312 available is very good condition. How easy of a swap would this be, I know I need to use my distributor w/tach drive and I think my Holley carb. Anything else that might need changed or swapped. BTW, the engine in the car is not the original engine that the car was born with so the motor exchange is not a big deal. 

1957 Thunderbird 312 Fordomatic