[Goober]

Ok now this may seem over the top. I needed a way to hold my petcock steady and level while I drilled a pilot hole through the rivets. This is my sixth petcock rebuild.
I traced the mount holes and outline of the petcock. I used 1/2 inch spade bit for the mount bolt holes and three for the outlet. Then I used 3/4 inch spade bit for the center, center left and center right body position. Then I bolted the petcock to the jig.
I bought a petcock in unknown condition and dirty as you can imagine. After all this I plan to use a drill press to ensure a straight hole through the "ears" of the petcock rivets, tap the holes for 6mm x 32, and replace the seals!

 

[retro]

Hey thats really fancy!

I just opened my petcock last week without a holding device. I drilled just the heads off of the rivets, filed the rivets ever so slightly shorter (so they will still work as alignment dowels, but allow the cover to be fully tightened down), then drilled and tapped for #6 screws. Luckily my rubber parts were in great condition, so I just flipped over the 4 holer piece to wear on the new side and slathered silicone grease on all the rubber parts.

Looks like you intend to fix a few of them.... good thinking!