Hey guys thanks for all the discussion pertaining to this. I just signed up on Stovebolt and this was my first post and will hopefully become better versed in the terminology and more detailed as my project progresses. I referred to the rear cab mounts as "shackles" only because that is what the vendor called them otherwise they were just rear cab mounts to me, albeit odd looking ones.
I never would have consider the condition of the front support effecting the rear of the cab but will definitely take a look at it in the morning. Unfortunately, I have not leveled the chasis and have simply been working on the disassembly with the tires still on the pavement.
Prior to disassembly I did notice the passenger door was a difficult to close but didnt connect it to the possibility that the source of the uneven gap in the back could also be the cause of the door fitment.
I really appreciate everyones feed back. The only thing I regret about joining the website was not doing it before I laid a hand on the truck.
The truck is a 1950 3100 that I purchased a few months ago and have been slowly working on it when time permits.