yeah the block on my m880 is like 3" or maybe 3.5" i forget exactly.
mine does have a pretty aggressive rake with factory springs all around.

my truck has the factory rearend in it, dana60, so the axle tubes/spring perches might make the height of a 1/2 ton truck a little less than on an actual m880.

i still think you'll end up with some rake, it'll be fine though. get the rear together then decide what you want to do with the front.

btw there should be a metal plate on the dash in the m880 that list the weight ratings and all that stuff.