Welcome to the Stovebolt Tony!
A '54 would have been a GMC 248 originally. and the model would be 100 not 3100. The 235 and 3100 model designation are both Chevy.
If its a GMC motor it will have a serial number behind the distributor near the starter. The first three characters will be the engine size.
My '55 1st GMC has a 248 from the factory, but had a GMC 270 when I bought it.