You need to contact Kelly Coefield, aka, panterror here. PM him here.
He did an entire project of casting intake manifolds and manufacturing throttle bodies to fit under the original engine cover on the Pantera.
What he did sounds suspiciously like what you are planning?
He may have enough parts left for your project.
I'd suggest that you freeze this project now until you speak with him in detail.
He already made an intake (had them cast and machined) just like you are describing making. He probably has some left?
I found this additional information for contacting him. He is now know as the "Ford Autolite Guy".