Perhaps my trans is not out of a truck at all. Did the truck transmissions have 2 shifter mounting bosses? one forward and one rearward? Mine only has one mounting boss in the forward position. I'm sure it's an O/D trans, it has the 5.125 bearing retainer and the large 308 bearing behind it. So, in answer to your question, I had no modifications to perform.
thanks again for all your advice.