[dsraven]

looking at the pics you have posted I would say once you get the frame checks done you may want to think about a stout trans cross member to keep the frame rails from springing between the cab mounts. the old original cross member was pretty stout and also held the weight of the engine and trans since the engine was mounted at the front and then the bellhousing sat on the cross member leaving the trans hanging behind that. the original bellhousing, even for a v8 truck, was cast iron. possibly extend some frame boxing behind the welded on clip for strength and also to keep the frame from stress cracking at the welds where the clip goes from a fully boxed section to a channel section on the original frame. kinda hard to tell from the pics but it looks like that has been done on the pass side? keep in mind the issues this may make if you plan on a frame mounted brake booster. it seems like that frame transition area would be the weak link if there were to be one. frame flex will be the enemy here. a short boxed area would also lend itself to bolt on mounts for the trans cross member. just a thought.
nice job on the firewall from what is visible in the pics. I don't see a firewall brake booster hole but the pics may not go up far enough to see that.