Car Freq Mod?

[88-Fiero-GT]

I'm looking to run 3 ZZs at the same time. Has anyone been able to change the Freq in the chasis to something other than 49 or 27?

Can someone help me understand what to change in the chasis to get different Freqs? I see the crystal in the controller, but don't see the obvious item in the chasis to change.

What I would really like to do is to mod it to accept a crystal socket in both, then use the Xmod crystal sets.

Thanks in advance!