I've built a number of 406's and 383's with h-beam 6" rods and roller cams and have always used standard base circle. The only problem I've experienced was the first 406 I built. It had stock 5.7 rods and a small solid cam. I had to grind the cam side rod bolt heads to gain the necessary clearance. I'm pretty sure that most h-beam rods are profiled to gain the necessary clearance. You'll need to check it just in case.....