Oh my, I've been unseated as having the oldest TM on the Forum! *G* Welcome!
My TM is a 1986 TM25, so just one year older than yours. I went out and did some measuring and checked the sticker that has the weights on it. (BTW this sticker is only visible on mine when the camper is open, it's on the top of the lower wall above the electric cord storage.) I didn't have anyone to hold the end of the tape so this isn't exactly to the millimeter, but pretty close. *g* And the bathroom is the old all in one wet bath, pictures are on my blog - address in my signature below.
Manufacture date: April 1986
GVWR 3920
GAWR 3500
Tires F78-14C 14" rim
Lower box length: 16'
Upper box length - measured at the bottom of the shells, I couldn't reach up to where it curves out at the top and was too lazy to find the stepladder: 24' 8"
Bathroom width, door side wall: 40"
Space between bathroom wall and front of rear bed wall, under wardrobe: 21"
I really need to take this to the scales and get it weighed, that's really the best way to be sure what your weights are.
Hope this helps!