Engine swap choices 4x4 Hell

[Rednwhitec20]

Hello, I am in the process of rebuilding my 1971 k20 from the frame up. I am wanting to go fuel injected because it will be a daily driver. I am not too concerned on gas mileage but it can help. Right now I'm looking between a 4bt, 6.0 Ls, and maybe even and 8.1 ls. The 4bt will get great mileage but I'm not sure how much it would cost to lay down some decent numbers like 250-300 hp and 450-500 ft. Lbs. the 6.0 and 8.1 will get about the same mileage but the 8.1 is a monster and I will probably keep it stock for a while. I will be going with an nv4500 transmission no matter what the choice is unless I get a deal with a nice transmission included.