If you don't have any luck finding a manifold, check out your local salvage yard. You might be able to find a factory aluminum intake. I have seen some '80s era cars with them. They might not flow as good as an aftermarket intake, but you are already keeping your stock exhaust manifolds, so I assume you aren't terribly concerned about that. Also, the early 70's and earlier Qjets can be had with a manual choke. I am not trying to start the whole "my carb is better than your carb" debate, but I think the Q-jet is the way to go.