When I was looking for a TM, I was very curious about some of the technical aspects of TM construction. Sorry, these are not going to be picturesque!
One of the big questions, what years had metal framing? This varies, and cannot be pinned down to a specific year. However, you can check without removing any screws. Just peek underneath and inside one of the pocket stops. These are located where the lift arm attaches to the upper shell. There are 8 of these in total.
[EDIT - check Post #8 below for more info and another picture]
Not all wood can be eliminated. One place is for the bag seal, and this wood needs replacing once in awhile. It's hard to see as my camera was fighting with the bright sky and dark pocket. Much of the wood is rotted in this image and will need replacing. It shouldn't be very difficult. When the bag seal is removed, chip or blow out the remaining rotted wood, clean with dilute bleach, rinse well (you don't want bleach remaining on metal, it can erode metal). Then replace with 1x1 treated wood. Other's may have their own suggestions for this repair, but whatever solution, it won't be very bad. Nothing like what Maria went through!
Trying to figure out where those wasps were coming from?
Here is a good shot of the torsion bar. Tightening the bolt pushes on the short length of the "L", increasing tension on the torsion bar.
Here you can see how the shell is attached to the lift bar. There is a thicker aluminum plate which is attached to the aluminum frame inside. The outer skin is damaged on mine, exposing the inner plate. The tear here will not affect the function of the lifting mechanism, but there may be sharp edges so a stainless fender washer may be a good idea here.