Dave is right, leave S10 frames for S10's. You are kinda going at it backwards. Decide on the body first and buy that, then start mocking it up the way you want it to sit and design a rectangular tube frame to make that work.

The very best way to do it is to have your body, engine, transmission, front axle assembly and wheels and tires BEFORE you start thinking about your frame. Then build a mockup frame from 2 x 4 lumber to simulate what the steel frame will look like. When it looks good build the real one out of steel to the same dimensions.

Don