I know this will go over like a f#rt in church as others have done it but i dont think i would put a section in the frame unless i used another s-10 of the same material. Why not cut the s-10 clip off and weld it to your stock frame....i dont like the idea as i have stated before because they are too narrow but if your heart is set on and s-10. I have also seen guys back half the s-10 clip with 2x2 sqaure tube. It looked pretty good other than the front width.
I still would vote to keep your stock frame and put an crossmember under it.
If your like me with your shop(busy as all heck) you probaly would rather pay a little more and get it done in a day than have it laying around the shop losing customer work.
Man that truck is gonna fly with that GTA motor LOL your gonna have fun with that one