Steve's tool is a bit undersized on the 20 & 27. No problem on the
20 because there's a reasonable taper at the end of the pins –
not so on the 27 where there's only a rounded corner with a tight
radius; so you have to be really fussy lining up to get the first pin
in.

I would love a pin that's ground off at the end so there's only a
few degrees of arc. Then you could rotate to find if the next hole
is high or low. Fingers are not straight enough.

As for marks, I filed a flat spot where the cylinders line up, and a
notch at the maximum difference.

I find that feel works better than vision on a promising soaring
day because my eyes don't adapt quickly to under the turtledeck
when the sun's out.