A lot depends on how ol "old" is. Some very early ones had 4 pins. Little chance of them working. My first radio outfit had very chunky plugs, but on the "standard" 0.1 inch spacing. As mentioned, some manufacturers had their wires connected in a different order, some liked to have a polarising web on their plug moulding.
All of the 3 pin ones use the same signal standards, so once the wiring order is confirmed as being OK and any required trimming of the plastic plug housing is done, they will work with any modern radio. Provided that they are plugged in both the right way round and on, rather than in between, the radio pins.
Futaba did like to be a bit different with their signal standards. While everybody else used 1.5mS as the center, Futaba preferred 1.25. They also preferred to reverse the signal logic - Rest of world, forward was a longer pulse, reverse was shorter, Futaba the opposite. Going from a Futaba transmitter to a different one will probably involve recalibration of ESCs and taking off of servo horns and resiting them in the right place.