NEW TO THE SITE - just bought 1964 glendale falcon

First, welcome! If you are looking for excellent help and moral support, you’ve found the right place. You mentioned that the trailer is “gutted” and that there’s some new lumber. Almost all trailers of that vintage were constructed opposite of what one would expect. Gutting ruins the strength of the entire unit. In order to maintain the integrity of the box, the skins must be either lifted or removed in order to repair the framing safely. The inside walls continue down past the flooring rather than sitting on top of it.

I’m not good at explaining this. The first thing you need to do is NOTHING ELSE until you’ve looked at Mobiltec’s videos. It will save you time and money in the long run. Again, welcome. And please post pictures. We love pictures here!

Since you already own the Glendale you might try stabilizing the walls from the inside so you can safely pull the skins and rebuild it the way it was originally constructed. I'd buy a half sheet of 3/4" plywood, rip it lengthwise into 3" strips and with a framing square and some 2X blocks, attach a strip to the curb side wall where it meets the roof and attach the other end to the street side floor. Move the 2x back and forth until the wall is square. Do that a couple more times: middle, back and up front. Once the curb side wall is square to the floor do the same on the street side; upper wall to curbside floor in a way so you have 3 X braces holding both as square as you can. Now it's safe to pull the skins, J rails, roof, windows etc. Watch Larry's vids or Vikx' E-manual on pulling skins. You'll be able to see how everything went together originally and how cabinets etc. will keep repaired wall framing square.

I'm probably getting some stink-eye from others but in my opinion there are so few early Hams still out there that it's worth going outside the box to correct the "Gutters" that spend too much time on fakebook doing things wrong.
I wish you luck.