Would you swap a 454 for 6.0 to pull with?

[Kinghat]

I am approaching the purchase of a 77 crew cab dually. It has a 454/400. Plans are to shorten the bed and frame, go to single wheel, lower it 3/5ish but still keep it 1 ton, and use it to pull with. My question is, would you guys leave the drivetrain alone, or switch to LSx and 4L80E?

Second question, if you found a whole donor truck, would you keep the LSx's stock tank from the donor? I see most everyone use Blazer tanks on their conversions with either in-tank or inline pumps, but wouldn't it be feasible to use the newer trucks tank?