From what I have seen, nearly all the 350 diesels came with a TH350C. GM should have put a 2004R and something like 3.42 gears with them. They would have still got very good mileage and get out of their own way. Of course there should have been the extra head bolt added like the 4.3 V6 from the get go. I believe the V6 had 5 more hp and the T-50 was gone by 80 or 81. Olds also had a 150 hp 4.3 V6 version with tuned, long intake runners and headers, it never made production.