Crack in the battery was probably from freezing while discharged.
The common part of the gas, oil and temperature gauges is the 5V regulator. The factory one was mechanical, the rebuilt dash may have had an electronic one.
Sounds like you are on the right track.
Craig
PS My newest truck is a Ram 4500 Type 6. We have two of those now and a Pierce Type 3. We are pretty much a Pierce shop for the fleet.