Dave, totally agree. I have been searching online this past week or two to see how people are tackling cabs with rotted mounts and it seems the initial step is to get the cab oriented to the frame based upon FAM specs. Thankfully the FAM shows all measurements with respect to various points on the cab as well as the frame itself so it should be fairly straightforward.
I did see one example where someone used a 2x6 bolted to the firewall and then supported this at the correct height above the frame. I will instead set up an adjustable threaded support which will allow me to raise/lower the cab with respect to the frame to get it into specs and square. I will then tack it to the frame to keep it solid. I will then remove the floor/mounts and install new ones, checking that the frame/body combo have not shifted with respect to each other. I will do one side at a time to try to minimize issues.
Once floor/mounts are done it 'should' be clear sailing at least when concerned with the relationship between the cab and frame. I should be able to remove the previously added tacked in adjustable supports.
I can then attend to the cowl areas as normal. For these I will again do one at a time but the cab will now be bolted down to the frame via the newly installed floor/mounts.
If I think the adjustable support is something useful to others I will post some photos on here. Possibly a simple structure tacked to the cab at each front corner which incorporates a short 1/2 or 5/8 threaded rod, allowing it to be adjusted higher/lower with respect to the frame. I know the cab has slightly sagged at the driver's side front and so this will allow me to rotate the bar to raise it. If the cab is already at the right location at the rear which is likely, then I will only need to do this at the front.
Hopefully that all makes sense.
