WNG backaction is made of aluminum. We made a scale stick according to top action. Transfer the marks/spacing to backaction rail, then drill open with 3.3mm drill bit.
Tap for damper tray flanges with M4.7 thread tap, install flanges. On damper tray, mark 10mm from bass edge, then mark where flange screws will be. Drill with 3.3mm bit.
Tap all drilled screw holes with M4.7 thread tap. Apply tapping fluid for every 3 to 4 holes, without fluid, it will be very hard to tap and bit can break.
Mark where the tray ends, cut with metal cutter, clean cut surface with file.
Install damper posts and damper tray felt.
Use a square, check if under levers are square. If not, remove under lever, shim under screw surface, screw back, and double check.
Install damper tray. Note that a slot to clear sostenuto monkey was cut off on damper tray. Old and new backaction comparison. At least we don't have those swelled leads anymore.