Heres a photo that comfirms what you suspected that the 1-7/8th tube TTI's extend over the smaller (stock/W2 econo) center tube bolt holes. I used the caliper to measure the outside width of my inner 1-7/8 TTI header tubes and when compared to the econo bolt pattern it appears the tubes might half cover the bolt holes

Also a couple of shots with some W2 exhaust gaskets over some header gaskets and vice versa to help you determine how much overlap there is