Kurt,
I've used different things for different purposes. The rear radius rods on my roadster are made from 3/4" black iron well pipe, but it (the car) is very light and has a 4-cylinder engine. On my coupe I built NASCAR style "truck arms" from 2 x 3 rectangular tubing and mounted them with rubber bushings at the rear end and 3/4" rod ends at the front. I believe they would handle the 650 hp with no problem...

If you are dead set on a four-bar with that kind of horsepower, I would go with a heavy-wall chrome moly tubing that you can ream and tap to fit the rod ends without doing any welding.

If you are going to the Turkey Run, you might look for some pre-fabbed four-bar systems to fit your application...