Seeking advice intake manifold

The factory manifold is one of the better designs out there, and outside of the weight savings of an aluminum manifold over the cast iron factory unit, is pretty tough to substantially improve upon unless you start considering an AirGap type intake- and then you'd probably start running into clearance issues especially with the factory air cleaner setup. Then you'd really need to consider more cam to take advantage of the AG's capabilities.
The carb you have is a Carter Thermoquad, and there's people that will argue that it is one of the best street carburetor designs ever offered- and they're not really wrong.
My advice would be to keep what you have, and make sure it's all set up and functioning correctly so you're getting everything out of it that it's capable of.