Im about to pick up a 2002 2500hd ext cab 4x4 for a really good deal. As sits it has a 6.0 that sucked in some water, it still runs but has no oil pressure and the guy says it has a slight knock. i was looking into my options for motors vs rebuilding it and saw i can swap for ls1 and ls2 pretty easilly. what are pros and cons of doing this and how would it effect the mpg? i want it to have some balls and sound good. truck is sitting on 33" tires and might get bigger ones (idk if this matters).

Also any ideas on how messed up the 6.0 might be? since it lost oil pressure im assuming its going to need a machine shop?

thanks