[Irish1941]

If you're at $1500, just go to a 9" rear. Looked into building a 12b for the LS3 truck and it was same price as new 9".
For around $3-700 you can do a 9.5 depending what have on hand, dig up on the forums or can get from the wrecking yard.

I use 92-up k1500 heavy half 9.5 brakes. Drums are 6lug but that's what I use. Brakes all bolts on to any 9.5. Even e-brake works. I'd use the SS drums for now.
You could look at Trail Blazer SS rear brakes with different rotor.

Anywho.. here is some axle numbers for you.
92-98 K1500 9.5 axle is 33.1/4″ long - 6 lug
90-93 SS454 9.5 axle is 31 9/16″ long - 5 lug (correct pattern)
81-87 C10 10 bolt axle 31 5/16″ long - 5 lug
79-87 C20 9.5 axle 32.3/4″ long - 8 lug

So looking at those, to get to correct 5 lug width you'll need to cut housing tubes down and re-weld backing plate mount back on or use filled/drilled 6 lug axle and 1/2" spacer behind backing plate. Downside in your application on last option is rear gets wider overall by nearly 4". Great for 4WD not so much on street truck.
Hope this helps.