That's interesting about the keypad rows. At those quantities, the cost savings on a simpler PCB must have justified the redesign.

Good news/bad news- I got the 1976 version, but some plastic stuck to the die:

I'll try to clean it off without damaging the bits below. I transcribed as much as I could. I see lots of similarities, but lots of differences.

The die from Entex Space Invaders also stuck to the plastic, and it took a lot of heat to get it free. The passivation layer crackled and obscured the die, which I've seen before. But previously I could still remove the metal layer with Whink and transcribe the bits. This time, Whink isn't working. So I guess the heat cooked the passivation layer enough that mild HF isn't able to dissolve it. I'll try some other acid.