Jim, I would have suggested getting an original Y-block pump and rebuilding it, but the repo parts suppliers are not offering Y-block pump rebuild kits. They do sell flathead pump rebuild kits, but I don't think those will work for Y-block pumps.
I do know that the new pumps made in china have two valves in the bottom, one of which I believe is a check and the other a bypass, not sure. But if the bypass valve malfunctions, you could be pushing tons of extra volume up to the carb. And I can tell ya, those valves in the bottom don't always last very long on the china made pumps.
As far as building a bypass system back to the fuel tank, that can be complicated, because you need to install an orifice in the line heading up near the carb inlet that is the right amount to cause enough back-pressure to fill the bypass line. If that orifice isn't small enough, you may still have an overflow at the carb.
The worst thing about a bypass line, is you need to take out the gas tank, drain it and dry it out enough that you can weld a piece of tubing on at the top rear of the tank that will also clear the car frame and trunk floor.
