Radio South is the place for this kind of work. <
www.radiosouthrc.com> Here is their web site piece about narrow banding:
FREQUENCY CONVERSIONS
The FCC requirements for "gold" is -55db sidebands at +/- 20Khz. An additional requirement is the frequency accuracy must be within +/- 1.5 Khz from center frequency. Most transmitters can be "gold stickered" at a cost of $15.00. Pro-Line systems are $40.00, due to special components needed to update them. Kraft systems are $50.00 for pre-1976 transmitters, and $25.00 for 1976 and later versions. Frequency changes are common in order to obtain a frequency that is less crowded or to move away from known interference at a local flying field. Costs vary from system to system, due to the price of xtals required for the change. Most newer systems use dual conversion xtals in the receivers. Prices vary, but most Dual Conversion systems are $49.50 (tx and rx, including tuning) to change. Single conversion systems are usually $39.50.
I still like the older Futaba Txs, especially the FG series. If I had a good one, I believe I'd let Tony gold sticker the transmitter and get a new flight pack to go with it. Although Curtis is right, the new radios are so cheap and reliable....