You need to look at EVERY part to make SURE they all match. Just because the set was made by Libby, doesn't mean someone didnt upgrade it, sometime in its life.
As a matter of fact, that's why there is not a kit available from Libby. The military went away from the Libby system for a good reason.
When you say the regulator and pot are the same, you mean the pot is a 10 Ohm pot, right? And the transformer has what part number? Sometimes it's on the bottom, or right side, I think. In any case, the part number is there. And you need to check it and the Pot IAW the TM, as well as the Regulator. You don't know who they bought it from. Someone who tried to use it with a TRC system, and screwed it up. You don't know in what condition it was in before it passed into your hands. IF, all the part number match up, then TEST, it and not just once.
And for goodness sakes, don't forget the fuse and holder if there isn't one! You will hate yourself for forty forevers if you shoot the exciter rotor in the butt because of no fuse.