Please show us pictures of your equipment and process to enlighten us.
To the OP here are 2 examples of this process both of which I consider primitive and painfully slow. The first is done on a milling machine with a horizontal attachment:
Rear Seal Conversion for 216 235 261 to One-PieceThis example is done with line boring equipment…about ¾ down the page.
https://41chevystreetrod.blogspot.com/I routinely modify mud pumps approximately the size of a stovebolt block from NPT to ORB ports so this easily fits in my work envelope. I’m tempted to pull one from my stash to demonstrate (in real life) the process with modern machine tools.
