I like the LS series. Obviously any other first Gen small block will wake that thing up. Go vortec 5.7 and bolt it in.
Or, here is another crazy idea. You mention sand and weight and such. Assuming an all aluminum big block is out of the budget, have you considered a Cadillac 500? They make gobs of power, big trucks like them, usually they get better mpg than a bbc, and they are approximately only 50 lbs heavier than a SBC, lighter if you go with an aluminum intake.