Well, sort of late to the game with this info, but I did call TTI when I got some free time to get their recommendation. The gentlemen I spoke with literally said: "...if over 600 hp then use 1-7/8" pipe...".

Even when I asked him for the "room to grow", it all came down to that seemingly magic 600hp mark.

Alright, a bit weird I think, because as I've been scouring the net tonight trying a learn a bit more about this, I am universally seeing that 600 level being more of a 500 mark. Again, these are just numerous posts from folks like you and I.

I did come across a decent Header Ho-Down article, where 4 different sized pipes were compared. Even on a smaller displacement engine (that was a Chevy 383) it appears the big 1-7/8" primary pipes posted some impressive dyno numbers throughout the combo powerband. So seemingly counter-intuitive to the "smaller primary pipe nets more torque".

How is the clearance with the 1-7/8" header install on a SB look like?