My understanding is that the F4B is still a pretty good design by today's standards. However, the RPM range supposedly does top out at about 5500, however such things are spec-ed.
Are you familiar with Tim Ronak's great tech article on
www.tigersunited.com about Building a 350 Lunati? Fabulous detail I relied upon extensively in my 347 project. He details and discusses an intake manifold modification that should help you get an additional 500 rpm up to the 6000 level. As long as you have the manifold off, you might seriously consider making the mod to your F4B.
A suggestion regarding gaskets. Measure how high and wide the head ports are. On Summit Racing's web site you can narrow your search down by those parameters and hopefully get a close match.
FWIW, my aftermarket head's ports are 1.10 inches wide and 1.975 inches tall. I found a Victor Reinz gasket set that is an almost perfect match to that. I ended up using a Nibbler tool from my local electronics parts store to enlarge the gasket ports at the top by about 1/16 inch. The gasket set part number is MS15202x and I found it at a local Carquest store. I have no idea how that would work with your heads and the F4B, but if your heads have that configuration, it might be something to consider.
As for port matching, you might see if the F4B port pattern is smaller than the head pattern. Make a heavy poster board "gasket" based on the F4B and overlay it over the head. If the F4B's pattern is smaller all around, you could just enlarge the manifold ports accordingly. That is what I ended up doing with my aftermarket heads and a different manifold, belatedly after the heads were installed. I had been in a rush to get the motor put together at the time and then had to put things on hold for a while...
Hope some of that helps.
Gene