Frame strength questions 10 vs 20 vs 30

[notchbackgta]

I recently bought a 69 C10 Suburban that I want to make into a 4x4, but it has a coil spring rear. I just missed out on an 82 K30 that I was going to use for the frame and suspension under the Burb. Finding another one in the same price range, was only going to be $1,400 running and everything, is going to be difficult with low rust in this area.

I do have a frame from the same gen 67-72 GMC c15 with the leaf spring rear that I was going to put under my 69 C10 pickup since the coil truck frame has a few problem spots now. I got it with the the really nice bed that I needed to complete my truck

With what ever frame I wound up using under the Burb, I planned on boxing anyway. I plan on putting a diesel engine in the Burb in the long run and using it as an expedition rig(ish), so it will probably have lots of other stuff that will make it pretty heavy.
My question is, should I hold out for something better than the C10 frame, or will boxing that be strong enough?
Thanks