As I understand it, both are one-act versions with essentially the same major changes -- the whole Who Military subplot is cut out.  The difference is that the Jr. version is intended to be performed by kids, and the TYA is meant to be performed (primarily) by adults FOR kids.

That said, I'm currently in rehearsals for a full version that's going to be using recorded accompaniment ... apparently it's available, though I've gotten the idea that it's being provided by a third party.

That should be fine.  It's not a terribly demanding score vocally, either for the chorus or the principals.  If you can come up with a male and female trio who can handle harmony, you should be fine.