The 351C guys are over on the Network 54 site:
http://www.network54.com/Forum/119419/
I have a set of Ford Motorsport "B351" heads for my car. I found a unique manifold for the hi-port heads. Just dumb luck that the intake popped up on e-bay just about the time I pulled the manifold off to modify my linkage. Here's a shot showing the difference in height of the intake runners:
When I initially put my car together, I had two sets of headers made, one set to fit the stock BOSS 351 4V heads, another set made to fit the circular ports of the B351 hi-port heads.
Most of the 351C Weber intakes are made for a Pantera with a cable throttle linkage - I wanted a shaft-mount throttle down the center of the intake (like the old Cobra stuff), so I had another boss machined up and welded into my manifold:
The old manifold, with just a center boss is on the left, the new hi-port one, with an added boss to the rear, is on the right.
Sorry, no extra manifold to sell. Keep an eye on e-bay, maybe you might luck-out like I did.
Jeff