The Astro does have 4.3 V-6 power, 700R-4 or 4L60 OD AT, and either rear or AWD. True they are 5 lug wheels. The Uplander didn't replace the Astro, it replaced the Venture, which both are uni-body, front engine - front drive (and some Ventures were AWD).
The last of the Astro vans did 6 lug wheels, and they looked the same as the Silverado 4x4 trucks.
I thought the Astro had a full frame like the S-10, but I was wrong, sorry. But I'm sure the running gear, and even AWD assembly would bolt to an S-10 frame though.
