I would agree. Looking at tables of dimensions for schedule 40 pipe shows an outside diameter of 1.900". I went with 1.875" primary tubes. That provides only .0125" of clearance added when switching from the pvc to the stainless tubing. I thought I measured it with calipers and there was more difference than that... but? I cant even say for certain that there wasn't some tension in the mock up pulling the #6 tube further toward the starter after everything was unbolted, as it was contacting the starter and I didn't do a whole lot of yanking on it to see if it was a little bound up.
Then throw in movement of components of the mockup during shipping, regardless of how many screws I put in to hold it together... It had to survive a trip from Washington state to Minnesota with who knows how many transfers on the way. Then you have to build a welding fixture to hold all of the new header components in the same location as the PVC mock up parts, cut and fit each change in direction of each tube so it all fits correctly, then finish weld everything hoping the heat does not pull anything too far out of line. Add to that a very restrictive final install... Cant really complain too much. If I had chosen 1.625 primaries it would have helped. I could have routed one or more tubes out of the frame rails and into the fender wells to give a little more room. There are other configurations that would have been more complicated but provided some wiggle room. The dimple will cost me zero horsepower. The only downside really is that I feel compelled to ceramic coat the headers to help prevent heat soaking the starter, which adds cost to what is already an expensive exhaust system. I could have saved some money by going with mild steel instead of 304 stainless, and gone with formed collectors rather than merge collectors for those of you pondering a similar project..... The price difference in materials and components would probably offset the cost of the coating, which is $345 for a pair of long tube headers by http://performancecoatings.com/ in Auburn WA.