I have seen that fuel block. But I think it's a custom piece, as I'v never been able to find one.
You need some kind of cross over or return at the other end of the fuel line. Otherwise the fuel will dead head, and that's not a good thing. Ideally, you want fuel flowing through the rails.
If you use a FPR that has two inlets, you can bring a return line back from the end of each rail. Something like Aeromotive.
You can see how I did this with some braided line. But the radius was too tight, and the hose eventually failed.
Then I looped it like this. The radius was big enough to maintain integrity. But every time I wanted to do something with the distributor, that hose got in the way.
So, eventually, I went with a pair of 180* fittings, and individual return lines back to the FPR.
My other thought was to use some 3/8" hard line, and loop it around kind of like a highway cloverleaf.