"Welding to the frame is a no no. It will cause the hardened steel to crack. "
That settles it. You had me at "crack". Got my attention a little better than "temper", or "strength".
" What about a small box beam spanning beneath both sides of the frame and then bolted up with U-bolts? No drilling or welding on the frame at all."
This is the direction it looks like I will go.
Thank you everybody for all the excellent info