There are others on this board with much more FE knowledge than me, but I will try to help. What I'd be concerned about is the dimensions of the ports in the heads and in the manifold where they will come together. Ford had several different sizes of ports in the FE series motors. I would measure the port sizes in the manifold that you intend to use, then get with Edelbrock and get the exact port sizes of their heads and see if you have a match. If the ports in the heads were a little bigger than the ports in the manifold, I'd go ahead and use the tri-power manifold. The air/fuel mixture will slow down a little as it goes past this interface, but I don't think I'd worry about it too much. Now, on the other hand, if the intake ports are bigger than the head ports, I would have a decision to make because I wouldn't run it that way. The intake fuel/air mixture will encounter a ledge in this case and you'd experience considerable turbulence in my opinion. I'd either go with a different manifold or port-match the heads to the manifold.