dumb rear end question

[baz-r]

ok i have my sierra ready for the chop and now im on sorting the chassis.

all i need do is make my mind up on tube and cut , flat pack , fully welded semi or full

welding in no prob its just the hassle of sorting the little brackets etc
it seems that by the time i buy the cut tubes the plates and the brackets im not that far of the cost of a chassis in welded form or am i wrong?

so i see some of the flatpacks and the welded chassis come in the ally or fiberglass back end so what is the diffrence? is it just the round tube frame that makes the rear of the car is ommited?
or is it a bit more than that?

if any of the suppliers could pm me on whats fitted and not fitted to thair welded chassis kits that would be realy good.

thanks of all of your input so far guys