I’ve gotten better at doing this so I thought I’d show and tell what I’ve learned. This is all in the Paterek manual but here is my way of doing this with the addition of a fixture. Just need a hacksaw, needle-nose pliers, 6″ and 8″ flat files, and a 10″ rat-tail file. It helps to have a Park Tool AV-4 or a similar axle vise grips but soft-jaws should work too.
If you need to because of tire clearance, crimp the chainstays first, then slot them before mitering for the bottom bracket. The hardest part of slotting the stays is making sure the slots are in-line with the existing bend of the chainstay (if you’re using s-bend or single-bend stays and not bending them yourself), and at the right angle. I like to use my Sputnik chainstay mitering fixture for this since I can load up the stays in their tubing blocks and draw the outline of the slots while the stays lie flat on the fixture. This also makes sure that you have the correct spacing for the rear wheel and correct angle of the slots. I’ve tried it by eying it while holding the stay against the BB and dropout while in the frame fixture but that’s not as accurate (or easy) as using the CS mitering fixture. It’s awkward holding the stay while making sure everything is lined up and then drawing the outline all at once. If someone has a better way to do this, please let me know!