Whats wrong with the LQ4? You have to realzie that the LS motors arent like the old SBC and need a rebuild every 90k miles . I had over 230k miles on my 5.3 when I pulled the heads to replace the lifters the cylinder walls still had factory crosshatching. The only thing "wrong" with the motor was some carbon build up on the pistons and in the combustion chambers of the heads.
Also the cost of a rebuild wont be as high as you think its gonna be. Unless there is something MAJOR wrong in which case you could probably find another pull out in a junkyard for less than the cost.
I think 6.0/80e is gonna be your best bet. There is a reason that GM stopped putting the big block in the 3/4 ton trucks and started using the 6.0.