Big block Cuda headers?

I checked out the B body header install in an A body that's in the Tech pages on B B Dart's site. I need bigger tubes than the 1 5/8" that TTI sells. Has anyone tried to fit B bidy 1/7/8 or 2" under chassis headers in a 68 Cuda?
Ive got a 383 4 spd, namual steering 68 Formula S & have a 451 stroker (400 block), w/ Eddy heads, that's going in. We've moved the entire rear frame rails in 2 " on each side & will also have to modify the exhaust system to fit. Any recommendations on headers? I saw a company's website that makes custom headers for $1200, but that's out of the budget.