I agree with Mike.
If you can't go Pontiac use the LS engine. Those swaps are a little more popular with less flaming when put in a FGF. Afterall it is a "modern" engine vs the traditional SBC which does look like hell in a FGF.

But don't dismiss the 350 Pontiac, very good engines with the right heads and intake. You can easily match a 400's and even come close to a 455's hp depending on the builds, just not it's torque.
It you were to use a 4-5 speed instead of the automatic you'll be more than happy with the 350's street performance. I drove a 17 headed 350 4 speed for years, pretty potent street package.
I'm running a 350 Pontiac in my Road Race car as well.