Couple of tips for dummies like myself. Yes, you snap off that top and bottom part of the PCB.
Always test every single key before you build! I had 3 diodes on my TX-65 that were not properly set. Two of them responded to some flux and a hot iron. The other one had to come off completely. And yes, diodes are polarized. And yes, these DO have markings, you just need a good amount of light to see them. They are printed (debossed?) in the black. You'll see two vertical lines and a "W1" if you look very carefully. I removed the diode, added flux, reseated, and with a smidge of solder on the iron tip, I touched it to the diode and surface pad.