What model COE is it, and or what is the wheelbase?
The 1/2 ton frame is not very simple, it tapers from one end to the other. As crenwelge suggested a 3/4 would be a better start, and I'll suggest a 1 ton. They are both straight starting at about the seat (just like the COE frame), and would be simpler to bolt the COE cab riser to.
I think that the 1/2 ton stuff would be a little undersized, brakes included. Not that the COE cab is much if any heavier than a conventional, just I don't think it makes sense to go from something so substantial down to itty bitty parts.
Try to visualize the truck a little lower to the ground and with smaller tires on it, you may think its just fine, and if so then go for it.
I think because of the small tires and the large fenders you'll have to try pretty hard to make it look good.
Grigg
