LEFT: The fuel pump when factory made had a core made for the bypass tube as can be seen here 1, in machining a solid block casting I had to drill this section out, as can be seen on the photos as we go.
Area 1 is the cast bypass tube, 2 shows the two check valves, 3 shows the plunger spring, this is tapered. 4 is the intake tube filter, 5 is the pump piston, 6 is a 1/8 NPT square head plug for draining. 7 is the fuel line to mixer. 8 is a breather hole, around 1/32" to prevent air locks ( I guess), 9 is a hole to allow excess fuel that bypasses piston to flow back to tank.

Above: The pump bore was first drilled with a pilot drill, then a 39/64" drill, then reamed to 5/8" with a parallel machine reamer. I got away with out using a steady by taking it slowly. The 3/4" mounting thread was cut first, then I made a jig to take the pump by screwing it into it and then held that in the lathe. Griping the jig tightly rather than griping and marking the pump body in the chuck.

 

1/4" holes were drilled into the bypass tube as they were not cast into the reproduction casting.
One hole goes the full length of the tube and two from the side, as can be seen here.(left)

The photo on the right shows the hole that goes the full length of the body and also the non return valve insert pressed into bottom of the pump.