Now which do you have?
1 1/4" Flange , 1 7/16" Bore
or
1 1/2" Flange, 1 11/16" Bore
Flange is the c-to-c longest distance on the throttle base mounting holes.
Bore is the big hole in the bottom of the throttle base.
It's hard for me to recommend which manifolds you should use on the rebuilt head. There is plenty of personal opinions and hot rod articles on what works best for a 292. I've found that intake and exhaust manifolds on an inline 6 can take time (heating & cooling cycles with retorquing) to settle in and not leak so I like to do it once and not mess with it again. Since you already purchased the new manifolds, I would use them.
Your engine break-in needs to be uninterrupted and another reason why I recommend using a known working carburetor. You may be busy fixing leaks, tightening loose bolts, while keeping an eye on water temp and oil pressure.
