I wold do the 318/392 unless its an eagle crank, if that was the case I would build a 360 for TQ.

I built a 360 magnum for a 97 dodge 2500 and with a mild cam upgrade from Rapid340, EQ heads and steel shim head gaskets it pulled great and mileage was the best I had ever seen in a 3/4 ton truck, I borrowed it a few times and checked as I didn't think he was checking it right. Tight quench and as much compression as your fuel can handle are your friends.

If I was in your shoes thogh I would be very tempted to go 392 poly if I could find a 4bbl intake.