If you can find a Hitec Spectra module on 75 you can just swap it out with the 72 plug in module in your radio.
But they have been discontinued and hard to find.
This will give you a synth radio.
DonO did this in his 9cap and 9 zap.
I have one in my Multiplex Profi too.
As does Jeff. BD.
Futaba also makes a FSS module on 75MHz that's the exact same size as the Spectra but with the added bonus that the "channel change" dials are on the back face of the module instead of the side. With a Spectra you have to extract the module every time you want to change the channel, with the Futaba module you just have to turn the transmitter off as the dials are right there. (For some reason the folks at Futaba claim their module will only work in the 3PK radio, but I've been using them in my 9Z and W-FLY 8 for a long time now without a glitch.)