Unless your frame is shot, there's really no need to replace it. My '48 sits on the original frame but has four wheel power disc brakes, modern hydraulic shocks, a 3.73 limited slip rear and a T-10 five speed with overdrive. It's lowered four inches and has a monoleaf front suspension. It cruises at 65 mph with the engine at 2000 rpm.
The only fabrication was creating new upper mounts for the front shocks, having a driveshaft made and reversing the rear spring mounts. The rest bolted on.
Here's the truck:
BeforeAfter - front viewAfter - side viewAfter - rear view
