Of course I did just that. And that worked flawlessly. Which totally suckered me in. After that I built up the bar on that principle and found out that the variability resulting from very small errors in cutting and drilling was enough to cause some of the solenoids to bind. Re-doing that took a lot of time but the end result is much better.

The essential dimensions are: hole: 6.05 mm (drill 6 mm, it drills a tiny bit larger), pushrods about 5.72 mm. That gives minimum friction. But you can't buy 5.72 mm rods so you end up buying 6 mm rod and then sanding that down for every key to the right diameter. This is not the most precise process so you'll end up with 5.72 +- a few 100th of a mm. And then there is the humidity to deal with.

In the end I simply took a slightly larger bite out of the back of the action so it would have some more room between the edge there and the row of pushrods, that took care of any precision issues with where the holes were drilled and I matched each hole to it's rod individually based on how much play there was at the top, which is fairly easy to measure (deflection left/right).

The failure modes are: action not far enough back, pushrod will push the key up and then go right by it jamming the stick, pushrod can slip into the space between the plunjer and the wall jamming the stick and front row pushrods binding against the action. And because this only comes out when you have assembled everything it takes some time to analyze and fix.

What did not help is that the action itself is highly irregular, both in force required for a key to activate and in dimensions per key (especially horizontally), this made each key a unique item and my test key ended up not being representative enough.