Re: 700r4 auto tran.
I am not familiar with a 200R4 tranny. However your 4.3L V6 out of the Astro van was attached to a 700R4 or 4L60E tranny. The 4L60E tranny is an upgraded 700R4 tranny. All the gearing is the same, the tranny length is the same, etc. One of the differences is electronics. The 4L60E is computer controlled. The 700R4 only had a computers to control lock up the torque converter over 45 mph. The 4L60E took that further, all gears shift points are computer controlled. Both trannies can be built to handle up to 450ft pounds of torque. You did get the computer with the engine correct?
Any 700R4 tranny attached to the 4.3L V6 or any V8 engine will work. They all have the same bolt pattern. Now which vehicles did/does the 700R4/4L60E tranny come in. Chevy put them in all SUV's, 1/2 ton trucks, and some light duty 3/4 ton trucks. Thier is a difference between 2wd and 4wd models. The difference is the output shaft, it is longer on 2wd models then on 4wd models. If your going with a divorced t-case it won't much matter. But if your going with the t-case attached, get one from a 4x4. Might even want to get the t-case when you get the tranny, and the cross brace. It will make mounting the tranny into your easier.