350 chevy engines are getting harder to find,not to mention a good TH350 or 400 trans..back in the day they were easy to find,not so much anymore..the 7.3L diesel had its day and is impossible to find a good reasonably priced one now..most have over 250K and are on the way out..an easy swop would be a Cummins 6BT 12valve and an Allison auto,a lot of frame cuts around they come out of medium trucks and would fit without a LOT of mod work..the F350 would have at least a 4.11 rear ratio it would pull good with that rear..most good 6BTs go for around 4-5K sometimes with the trans.
try Adelmans (
www.adelmans.com) in Ohio,not too far from you. CommercialTrucktrader-(
https://www.commercialtrucktrader.com) 7.3L trucks going for 5K.
So whats wrong with what you have? hard to start or just plumb wore out? compression down,hard to start or is it an injection pump issue? The 7.3Ls are glowplug dependent engines thats for sure.Check those glowplug connections.
I don't know what your budget is,you could dump an easy 10K into an engine and trans combo and still be far ahead vs.buying a newer truck with taxes and registration all over again..it's a lot right up front but would pay off in the long run if you keep it and take care of it. It's a vicious struggle to own any diesel truck these days,but the 12V Cummins 6BT engine would be the best low-maintenance one to go with IMO
