Absolutely 1 7/8" hookers with 3 1/2 collector. i'm putting 2" on my Sonoma 406" and i'm buying a 2 1/8" weld up kit with 4" cpllector when the 434 goes in my Malibu this winter. I'm now running 1 7/8" on the 377" motor that's in the Malibu.
The 406" motor has the same lift cam as you have with flat top pistons.
Zip.