88-98 c2500 Frame swap in a '70 c20?

[chevy-aholic]

I have had my eye on another project for a while, and the other day at my buddies house I may have found it. His dad's got an old C20 that belonged to his father sittin in the back forty. The cab, right fender, doors, hood, and dash are in amazing shape for having not ran since 84. However the frame is in a pile of itself down underneath. I did a little measuring, and this is the 127" wheelbase truck (regular cab, long-step) so I got to thinkin why couldn't I just pick up a junkyard frame and shorten it? If I decide to do this truck the goal will be to make a 3/4 ton work truck to tow my other truck with once it gets finished. The nice thing is that if I do the swap, the donor frame would come with good brakes, rearend, and suspension (making the ride a little more tolerable for a DD). Also, it would make lining up a mild SB extremely easy seing as tho no new mounts would have to be fabricated.

My main question is, if this seams like such an easy task, why doesn't it seam like many people do it? Am I missing something major here? I have no problems with shortening a stock frame (seeing as tho I completely rebuilt my 91 frame from the door seams back without any real headaches), and I think it would be the cheapest and easiest way to create a classic looking/modern driving truck.

any input is highly appreciated. thanks in advance.