I complain to SWMBO about not using a real browser. I should heed my own advice. There was supposed to be a post in response to -dev that said "Nope. Doh." facepalm
Yes it works now, with the ground connected.
The original plan was to have both Arduinos connected to the same computer, but the IDE couldn't handle having two serial monitors open so I focused on getting setup on a second computer and completely missed the grounds no longer being connected.
Thanks all (and -dev).
Next thread. Modbus RTU over AltSoftSerial, direct connect of two devices at TTL level. One step at a time. I'll add the RS-485 modules and additional Arduinos later.
Until the next thread on this project. 8)