Since you're basically butchering the frame anyway with the 4-link setup, and it seems you don't have any intention of using the truck like a truck, go ahead and cobble up the top of the frame rails. I'd suggest adding some sort if stiffener to keep it from bending, but since it seems you're more concerned with looks than utility, it probably won't matter what you do as long as the final assembly looks good to you.
Jerry
