Thanks Everyone

Jerry, would this knurl do the trick:

https://www.kmstools.com/magnum-pivot-head-knurling-tool-3059

And just so I understand, does the knurl expand the entire piston? or, is the raised portion of the actual knurl what creates the larger diameter? I ask because I want to be sure I am measuring the right location to check progress, do I measure on the knurl, or the smooth surface between the knurl?

Again, i really appreciate the help
Jeremy

1955 3600 father and son project