So, once I had the serial to the proper level, I ran the units back to back with a null modem cable. SUCCESS! The 300 baud data stream did exactly what it was designed to do.
Newer versions of the ARC-16 can go as high as 4800 baud. But my lowest speed unit is at 300 and it limits what other devices can use for rate. These things used to run at 110 Baud, just so you have an idea about speed that was considered workable for control of Radio Transmitters.
Now came the time to use my trusty serial to IP converter to make this thing continue to operate in the modern world we live in.
I've already written up the Comtrol Devicemaster on another project. I know there are less expensive options available, but I've never had a lick of trouble with these. When doing diagnostics for what's wrong with a service or "where's the data?" these things have a web interface that make it very easy to find out what is the issue.
Wash, rinse, repeat. One on each box. Then test. No trouble at all in the 24 hour test on my bench.
One last thing. The centralized unit that is to operate at our main studio has 2 modem boards. This is the Gen 2 of the wiring. Why do Gen 2? Well, thanks to a desoldering iron that wanted to go stupid, I couldn't get the chip socket out properly and decided to source the wires from other places on the board. I realize I could avoid the board altogether since JP3 holds all the data lines I require, but I'm trying to keep things neat with the MAX 3232 board, and the hot glue doesnt' hold to the painted case as well as it does to PC board.
That's it. Feel free to comment.