That 2nd board is now more-or-less fully assembled, and I built up a 3rd board with an ATmega1281 (same pinout, mostly - sort-of a superset.)  The SMT soldering is getting easier with practice (go figure!)  The 1206/0805 LED footprints also work pretty well for some PLCC2 LEDs I have surplus of, so that's nice...

In the course of working on the variants/pins_arduino.h, I discovered that I'd mis-labeled the upper-right connector.  These are "digital pin 48-53" on the Sparkfun and newer boards, but on the old-style Wiring boards (up through v0004, and this one) this is a "PWM" connector that is paralleled with some other pins, and DP48 is the built-in LED.  So those have been changed, and I added "49" and "50" for the 2-pin PG connector.  I've adjusted the regulator package drawing.

Oh, I also stopped working on my variant, in favor of using https://github.com/per1234/wirino that another Arduino user had already developed.