If you find an FM 27MHz radio, you have a rare bird. A 2 channel one will almost certainly be AM. Provided that the radios both (receiver and transmitter) work, as long as the crystals really are a matched pair since they work at an offset frequency to each other, the system will work. Obviously there is a need to avoid boards recovered from toys - these often use the makers own signalling system, rather than any recognized standard. The only real difference between manufacturers was the shape of the hole for plugging the servos in, different makers liked to have their plugs a slightly different shape - nothing that a modeler with a knife or a file couldn't sort.
I wasn't denigrating old fashioned - far from it. The 2.4GHz world has seen an almost total collapse of cross-make compatibility, and with some makers, cross-model compatibility.
