The manual says after finish painting. That sounded scary to me. OK for the pros that do several a week, but I was sure there would be paint scrapes and bad words if I did it that way.

And Mitch recommended doing it before painting - so I did.

Then when covering the fuselage I asked Mitch if it was really necessary to extend the fabric to the fuselage tubes forward of the fabric spacers. He suggested not doing so might result in a slight displacement of the fabric spacers such that the boot cowl holes might not line up perfectly. Good point.

For whatever it's worth, if I had to do it again (and on my next CC ) it seems to me the best time to drill the boot cowl to the frame is after the fabric is on and shrunk but before painting. Doing it then would allow terminating the fabric at the forward end of the fabric spacers (Mitch said they were doing this at the factory).