I have a 4x4 65 El Camino that I built on a 73 chevy C10 frame years ago (not the right way to do it 🤣), I have since done a lot of mods using the 99-06 GMT 800 chassis that are used in the Tahoe, Yukon, Suburban, Escalade, Sierra and Silverado's and the way GM made those chassis universal to all of the models (whether 2wd or 4wd) is really amazing; the SUV version has level frame rails so making a car 4x4 conversion with those is much easier than the way I did it 30 years ago!
I will likely redo mine one of these days with an SUV GMT 800 chassis like the OP has, it would be MUCH lower than what I ended up with using the pickup chassis from the 70's (it looks like a kids rig now, which I thought was cool back when I did it 😁) but I would like to try and see if I can get it looking like it would have looked if a 4x4 was an El Camino option from the factory back in 65.
I have never messed around with the S10 chassis but I understand that they work well for old car chassis conversions as well, if I ever find a good deal on an S10 chassis I will buy it and experiment with that 👍