I have a 1988 chevy g10 van, 4.3 v6, with thm400. I also have a 1987 astro,4.3 v6, with 700r4. Here's my question...can I put the 700r4 into the g10 in place of the thm400?

The driveshaft will have to be shortend and the electrical will have to be hooked up for the electric downshift on the 700 but it is possible.

Check with your local tranny shops.

and welcome to AF