Hi, R2D2.
The 'framework' that you mentioned are commonly called rock guards. They help to keep dirt and rocks out of the lower track during operating and .to a certain extent, also help to hold the track on as well. There should also be 'through' bolts between the two sides with spacer tubes between the guards to help hold them in place. You can clearly see the outer ends of the 'through' bolts in your 3rd and 4th photos

Did you check to see if the bolts turn in their threads. If they don't, it'z gonna be a real PITA to get them freed up, replaced and tightened and they are RENOWNED for seizing up. Ditto with the blade mounts. If you plan on restoring those rock guards to anywhere close to where they should be, you will likely find yourself under that machine a fair bit.

Just my 0.02.

I think those nuts were on there and Cat built the tractor around them, they look good and frozen. There are a few missing, already, and I thought I'd need to burn the rest off, or at least heat them to red hot. I saw a roller or 2 rubbing against that rock guard. If it's important in keeping the track on then it would be high on the list to do. Otherwise, the dozer has plenty of other needs. It won't be used in a rocky environment, if that matters.

Hi, R2D2.
It'z not the nuts that you need to be worried about. Those rock guards rattling around loose will have destroyed the threads above the nuts, which means that, even if you can get the nuts loose, there won't be much thread left above them to tighten them up on. Ditto with the trough bolts and spacers.

The more the tracks, rollers and idlers become, the more the rock guards have to do to hold the tracks in place, even just when turning on uneven ground or maybe running over a small log.

Just my 0.02.

I thought that I would take the old stretched bolts out, and replace them with new grade 8 bolts. Since it sounds like it helps keep the tracks where they should be, it is now high on the list. One of the last things that I can probably do is re-install a de-railed track.

Hi, R2D2.
I suspect that you may have reached the right conclusion but be prepared for a LOTTTTA working getting those old bolts out so that you can replace them.

Onna related note, MANY years ago, I worked for a company DowNunda who used Stockholm tar as both 'Coppercote/Neverseize' and 'Loctite' in the one application when replacing bolts - seemed to work for them. Should be available from any good farm and ranch supplies outlet, often used for sealing horn stubs after de-horning cattle and for sealing the sawn ends of tree branches after pruning.

Just my 0.02.

Just my 0.02.

I bet those bad bolts will be difficult to deal with. Being under any machine is less than fun. Once they are pounded out after fighting the nuts, the holes probably won't want to line up either.
I usually put a "never seize" on anything I think I might need to remove. That bad tire under the trailer had the most difficult, tightest lug nuts holding that wheel on I have ever removed. They have "never seize" on them now. Try to imagine fighting with a cheater bar laying under a trailer with not enough room. The meaning of life came to mind.

Hi, R2D2.
I have worked under machines few times myself. I am RETIRED now.

Just my 0.02.

Click to hear a little RD4 grunt! Skinner 

I'm retired too, but this dozer may end that.

It has crossed my mind that the belt and starter attached to the pony motor flywheel... could that setup have been used to start the main engine? I was thinking that if the pony motor was not working would a starter spin the main engine fast enough when set up like this. I don't have the best picture, and I don't even know what voltage the starter uses, but if this would start an engine, I could see someone not fixing the pony motor. I know the starter was used to turn over the main engine when it was checked whether it was stuck or not. If starting in this manner could have been done, I'm sure this tractor would not have been the only one started like this, but I see no mention anywhere about it. If it is unlikely to start a cold engine, could it have been used to do a quick start of an already warmed up one?