Have you ever considered just rebuilding your engine and bore and stroke it to 383? Would be alot cheaper and not as much of a headache. Just a suggestion. You would end up with not power then the 6.0 and more then likely better MPG. Those 6.0 suck on gas. Everyone I know get about 10-12 City and 14-15 empty on the highway and these are stock truck not lifted.
Just something else you might want to look into.