We are all in the same boat with respect to finding the right headers for our limited ground clearance, high performance hot rods. The problem is compounded for applications that require larger than 1-5/8" primary headers. I have yet to find a company that can reasonably supply 1-3/4 or larger full length headers that also offer good ground clearance.
There is a great temptation to run a shorty or mid length header for best ground clearance, but the limited primary length creates a high risk of contaminating your 500HP-plus engine's intake charge. Pressure waves are an important factor in header design. And like any wave, exhaust gas pressure waves are bi-directional. Properly designed, these pressure waves can help scavenging, but pressure waves from shorty headers are more prone to contaminate the intake charge during camshaft overlap.
On a 300hp street rod, no one cares. Clearance is king and cam overlap is virtually non-existent. But for 500 HP and up pro-touring car, adequate primary length is mandatory.
But don't take my word for it. Read on:
http://headerdesign.com/extras/design.asp