I think I've said this before but this is a nice build and I appreciate you sharing everything. Also, I think you choose a good builder, one of the worst things you can do is veer off the course of what the 'team' your working with is guiding you on IMO. I'd trust what they told you to spec dimensionally for tubes. I also think given the parts you are listing that, the power will be well above 1000HP. I'm really eager to see the plumbing on these...If they are class legal you may do better with a fender exit collector.