Success!
Starting from the beginning...
I foiled the entire cowls, masked off the back and painted the yellow fronts. The yellow also got a coat of Dull Cote along the way.

Then I foiled over the yellow, overlapping back past where the yellow stopped.

The yellow area from front to back was 6mm, so I cut 3mm strips of frisket film. I put it around the cowl, starting at the separation line from yellow to bare metal. Then with a hobby knife I made a cut on each side of the film, cutting through the foil. On the front edge this is the line between the front and back row of squares, in the back of the film it's the separation between the checkers and bare metal.

Then I used a piece of the 3mm film to lay out the checkers on the front half. I layed it on the cowl squarely, made a cut through the Foil on each side, lifted the film and made my way around the whole cowl.

After cutting the front half.

Then I lifted the strip of frisket film off the rear and cut the back row of checkers free hand.

I masked off the bare metal back side again and shot the black, then obviously peeled off the remaining foil to reveal the yellow sections. I'm happy with it!