The FMX came out in 1958 as the "cast iron Cruiseomatic" It was used in pretty much everything in one form or another for many years. Studebaker used it as the Flightomatic. It is heavy because it was built the old fashioned way, to last. They can be modified if desired, there are shops that specialise in these things. They are still used in vintage drag cars. Just remember when you change oil in them, they are the ONLY Ford trans to use type F fluid. It can be hard to find, however type F fluid was used in farm applications, so it's still very much available, just not in the "quickie" chain stores. DON'T use type FA, this was used in C4 and C6 trans only. They are not interchangeable. Type F fluid as some astute people will know is the auto fluid used in modified trans no matter what kind they are. The C4 and C6 trans are another story altogether, they need a lot of modifying for heavy duty use. The only drawback with these old trans is none of them have an overdrive. But you know, we drove millions of miles on these old trans with no overdrive, it is not really a mandatory thing, believe it or not.