[Mike C]

The big problem with the 2 wheel drive truck headers is that they hang down below the frame rails dragging on everything if the truck is lowered or subject to damage if using the 2x4 in a farm truck like environment.

4x4 headers exit between the frame rails since the crossmembers hang lower and the exhaust pipes run above them unlike the 2x4 crossmembers where the pipes run under.

I would be looking for junk Chevelle/Camaro SBC headers to test fit and then buying new ones when I found ones that worked. I always thought moving the V8 back to the 6 cylinder location might allow for 4x4 or Corvette headers to be used which would be above the frame rail. That way custom exhaust could be routed between the frame rails. I cut 4” pipe clearance holes in the trailing arm crossmember of my ‘69 so exhaust can be routed that way when I do big block swap.

I have not measured exactly, but C3 Corvette headers seem to be near identical to 67-72 4x4 truck headers.