Okay, I wired up the I2C interface to the LCD, connected the potentiometer for the speed control, and connected jacks for the key and the key out. Along the way, I found that I had labelled the I2C lines wrong, swapping the data and clock lines.
And, yesterday I created a keying cable to go between the keyer and the FT-102, and the radio keyed! So, I need to put it in a box.
I'm going to populate the second keyer shield first, though. I want to see if I can get rid of that big 100uF electrolytic on the speaker.
I populated the other board I'm building and the 22uF cap is plenty for the purpose. The sound coming out of the speaker is loud and clear. I'll retrofit the first board.