Here I'm going to show you how to modify a standard "dead head" Holley reg to a full bypass type.
Here is the stock regulator in pieces, you can see how small the stock feed hole is and why these things are capped to around 450HP.
Here is the retainer, spring and ball valve. The part on the far right is the seat for the ball and this can easily be removed from the housing with a small drift or a bolt used as a drift (punch). Remove them and throw them away.
Here is the standard diaphragm. Just cut off the pin with a hacksaw and file off any sharp ridges left from cutting it.
Here it is modified.
OK, next I put the housing in a vice and drilled out the housing with an 11.5 mm drill bit. You could use a 7/16. That port is a lot larger now
Time to make the new seat. I took this , stuck it in the lathe,
And made this seat out of it, The hole in the center is 3/8 or 10mm
I then pressed it into the housing with a soft ( alloy) drift so it wouldn't hurt the face of the seat. The new seat has a slight interference fit. You could do this with a piece of tube that is a snug fit in the new hole and some Loctite. Just make sure the tube is cut square so it seals good enough to the diaphragm.
I made the seat .100 thou high because as you can see there are stoppers in the original casting. If you are not careful , the diaphragm will contact these first before the seat and fuel will leak past the seat and there will be a poor seal.
Now just reassemble with the pressure spring in its original location. The old "Inlet" has now become your return to the tank. One of the "Outlets" is used as your feed from your fuel pump and the other "Outlet" goes to your carby. You can also splice into the fuel pump line and feed multiple carbs if you like. Remember you want to have a return line around the same size as your main pump line. Returning fuel like this puts way less load on your pump, keeps it cooler and usually quieter. Keeping electrical components under high load conditions is what wears them out sooner.