which models of Futaba radios? I've seen people state it works on the PJS, but are there other Futaba models with an interchanble module?

I understand the FCC deal, but then again depending on how you read their rules, we shouldn't change crystals in any of our radios either.

FYI:
As far as the FCC goes, it has not been determined to the best of my knowledge what extent the rule is being enforced. It basically can't be enforced by the way it was written many years ago. The "technical" wording of the rule is that no crystals may be interchanged for any other than what were originally provided in a Transmiter or Transciever.

The reasoning behind the way it was written is, as I understand the history of it, was to prevent some of the 11 meter band radio users from adding upper and lower sideband crystals to their common cb radios, remove the clipping diode, and this could allow them to increase their power and allow them to talk a long way.

In the case of our hobby radios, I don't think we'll see any radio police at our RC track as I don't think the output of our radios are powerfull enough to make a difference. However, I'm sure you'll be glad to know that our tax dollars are paying for some geeks sitting in vans all around our cities watching spectrum analyzers for illegal transmissions.