Exhaust limits/Carb choice

Good evening folks, and first post.

I'm trying to keep my youngest son from making many of the same mistakes I made 30 years ago on hist first car.

He recently picked up a '67 Dart with a blown 318, but the body is fairly straight and the car has an 8-3/4 Posi with 3.55 gear set and a 904 AT. I've donated a spare 360 to the project which was intended for my '37 Dodge PU. The motor is bored +.030 and is filled with KB107s yielding 9.4:1. The cam is a Crane H278-2 (222/234, .467/.494). The manifold is a Wieand Stealth which is a dual plane similar to an Edelbrock Performer RPM, but with a spread-bore flange.

I have two questions concerning the package:

1) At what point do I saturate a cast iron exhaust manifold set and have to go to tube headers? (The car came with a set of Hooker Comps which have a couple of flattened primaries which could be fixed. I also have a set of 360 A-body cast iron manifolds.)

2) We have both a 750 Thermoquad and a Holley 650 spreadbore double pumper. Which would be the better choice.

Thanks in advance for any opinions offered.

Cheers, Mark