Intake port tongues are normally epoxied in place and then a hole is drilled through the botton of the intake port so a screw can be sunk through the port casting and into the tongue to prevent the tongue from breaking loose.
However, rolling your own tongues seems ill-advised unless a flow bench and dyno are available to you. The 4V head is a well designed head to begin with. The 4V head & strip dominator work very well together as is (the dominator manifold uses the head's intake port the way it was designed to be used).
If you want a pre-engineered system along the lines of what you are considering Terry Parker of Australia sells intake port "tongues" that fill in the floors of the intake port, plus a very well engineered intake manifold designed to work with his tongues.
The AFD 4V alloy cylinder head has filled floors out of the box & is designed to work with Terry Parker's manifold.
My quick two cents on the 351C 4V. The 4V head is not a flawed design, it marches to an older drum beat, but it works very well as long as an engine builder understands what the motor likes and dislikes. As it came tuned by Ford there is no problem with low end torque or an overly abrupt coming on the cam at 3000 rpm; it pulls hard and linear from idle to 7000 rpm. Port velocities are good by older standards, just a bit low by modern standards. Problems with low end torque are usually the result of too much overlap, insufficient compression, ignition tuning or carburetor mis-calibration. A well tuned carburetor and a dialed-in ignition can normally restore low rpm response so long as the cam shaft design is not too far off; the 351C is a bit picky about camshaft events and its requirements are much different than those of an engine with small port cyliner heads. A 383/393/408 cubic inch stroker kit also helps bring the port velocities up to modern standards.
I also agree with Joule's sentiments, that messing with port tongues makes little sense when there are so many excellent small port cylinder heads to choose from. CHI makes a 4V head that is nothing more than their 3V head with the port flared open at the intake manifold flange to a 4V size port. It would mate with the Strip dominator out of the box. It flows about 315 cfm at 0.600" lift out the box too.
But if you just have the itch to experiment, that's cool, its not my intention to discourage you.
cowboy from hell