406 FE into a 1955 Ford Sedan
General rule of thumb...If it came with a "Y"-block, an FE is easily a direct swap, both have front sump oil pans. Biggest issue will be cooling, transmissions, rear end and headers. The modern 9 in. didn't come out until '57, so the factory rear may not last. Headers, as mention are available. Cooling is not that big an issue today, there are many shops that have, can recore your old or can make a modern aluminum replacement.
This engine swap is not breaking new ground, it's a fairly popular swap going back to the late '50's. The top loader makes it easier.
Both FE and Cadillac engines were very popular swaps back in the day.
[ This Message was edited by: Beoweolf on 8/13/05 7:21pm ]