Thoughts on a platform switch, fueling an '03 turbo in a 1st gen

Been thinking about the fate of my truck, the various speed bits attached to it, and the turbo motor build: I think I would rather invest in an expensive pro-touring-style build on a RCSB 1st gen platform than my extended cab 2nd gen. I'd still want to run the '03 4.3 turbo / NV3500 I'm assembling now so I'm guessing I'd need a stand-alone PCM/harness setup to make it work. 

Long term, I'd like it to be a super basic, capable auto-X and lapping truck. Street legal, fixed race seats, minimalist interior, cage, 3-link rear with disc brakes, some version of my current front suspension/brake setup to save $, fuel cell / blazer tank behind axle...

Any thoughts? Am I better off to finish on the platform I have?

You'll definitely be gaining a weight advantage going both 1st generation and RCSB. Wheelbase may not be as stable, but rotating more quickly could be an advantage? Probably not a huge factor overall.

Wouldn't necessarily need to be standalone as you could integrate many of the circuits into the 1st gen platform. It is somewhat undocumented territory, so you'd be breaking new ground. I'd been thinking for the last few years of passing the Blazer's 4.3 onto the long bed and bringing much of the 2nd generation platform, electrical included, along for the ride. With me selling off everything, but the Blazer, I'm totally willing to help anyone who would like to tackle any level of 1st and 2nd generation integration.

Another advantage of scooping up another truck for your big PT build is you can continue to enjoy driving the extended cab as is while fabrication is underway. Get the engine swap and any other of the major components done that you can and swap over the rest afterward. That would be the time to do convert the front to a true coil-over setup like we've all been dreaming about for years. 

I've thought about the stability issue a lot since my current setup is ridiculously easy to control on the limit. The length is certainly an issue for our tight auto-x courses but it's still not much slower than the firebird on the same tires.

On the coilover issue - I'm wondering if actually makes more sense in the end for my purposes to go less pro-touring and more race car, like the GM auto-X S10 build. Cut Z85 coils or similar race springs, spring jacks, some sort of HD circle-track style 10" rotor brakes and 15 x 10 Aero race wheels with slicks. Simple, fast, cheap (relatively). I need to talk to UMI again about the standard coil setup they have in development right now. I've never been 100% happy with the QA1's and maybe this would be a good time to start with a clean slate.

You have also gotten your spring and sway rates pretty well dialed in on that chassis. Might be more twitchy on the shorter wheelbase, but could be close with the same refinement you've done before.

Rethinking the front suspension is exactly what I'm suggesting and also what I'd be doing if I wasn't focused on getting the 5.3 swap running and driving. You could reuse the shocks even if they aren't in a coil-over configuration too. Although there are better coil-over options for the front of the 2WD, but to do them well seems to require cutting and fabricating at least a few things with the front frame. The 2 bouncing around in my head are beefing up and/or extending the upper shock mount and running a true coil-over without the spring pocket or cutting the spring pocket out flat to the frame, plating it and running a coil-over on the outside. I do like the simplicity of what you're proposing too and the hybrid coil-over setup we've been running has lots to be improved upon. Primarily, removing the side loading from the shock.

I'll likely do more serious mod/fab work than I have in the past even if I don't swap to a 1st gen. I don't drive the truck as much now so if I keep it, I'll park it and properly tear into it to do things properly.

My biggest problem with the QA1's so far has been spring rates but I've also never found the sweet spot for the single adjustment on the front (rear seems good).

The light weight is a real benefit of the gen 1. I feel like I've cut a lot from my truck already and it's still 3400 lb - not light. I'd love to get sub-3K.

imo ditch the truck platform all together and place your time and effort into something that can actually go fast

Tinkering with the truck doesn't mean I won't keep building up the f-body, which I think has the potential to actually go fast. The car will either be getting 275 Hoosiers or a square 18x11 / 315 Rival S setup soon.   

My biggest problem with the QA1's so far has been spring rates but I've also never found the sweet spot for the single adjustment on the front (rear seems good).

Both of my ideas above would be going to the typical 2.5" coil-over spring, so pretty much all the spring options there. Single adjustable can certainly be limited, but might be less of an issue with more spring rate options. Going outside the frame does push you to a spring rate more directly related to the wheel rate for better or worse.