You are probably not wrong about the FP-T7UAF. I was speaking in general terms, since I'm not familiar with most of Futaba's older products. I just got into the sport a couple of seasons ago, myself.

Your FP-T7UAF radios aren't even listed on Futaba's website under "discontinued systems."

The FP-R127D receivers that you have are made in a high-band and low-band version. It sounds like you bought a pair of high-band receivers, so you don't want to put any crystals in them that are below Channel 36. I believe it's possible to have the receivers retuned if you send them in to Hobby Services, but it's probably not worth the expense.

I did manage to find the owners' manual for your radios here:

http://manuals.hobbico.com/fut/7uaf-7uap-manual.pdf

"The crystal can be changed from the outside of the receiver case. Always use the Futaba transmitter/receiver matched crystal set to change the band."

Reading through the manual, I can't find any detailed information about the RF module or directions for changing TX frequencies other than the blurb above about using a "matched crystal set."