You know I was told before that you have to use futaba crystals in futaba receiver and hitec in hitec, but I know from my testing the futaba crystals work in hitec and vis versa,
I've only done this in my Cars and would not ever think of taking the chance with my airplanes

I have also tested the hitec 75mhz spectrum synthesized module in my 7uaf and 8uaf Tx,,also both work fine
Also I have used Futaba and Hitec receivers sold with 72 Mhz crystals with 75 mhz crystals in my cars and they too work fine

But again these are all Module type TXs so I guess I've never been in violation of FCC rules
I have been in violation when switch TX crystals in my cheap futaba T2PC AM TX,,,I wonder why they have the crystal slot on the outside of the TX and they sell crystal sets if it's a illegal to do so? Please no one call the cops on me or all the guys at the track,,, this goes on all the time,,,I guess we could blame Futaba for entrapment

I can't speak to the "Perfex" system being compatible with the futaba crystals, if the Perfex is Futaba compatible then I'd guess yes,,,Who makes the Perfex?.