MCT Serial board mystery - Can you crack the pinout code?

[drlegendre .]

Decided to take a good shot at putting my only S-100 serial board to use.
Figured the place to start was ID'ing the connector pin-outs so I could set
up a cable and begin the process.

Lacking any docs whatsoever, all I could do was trace out the PCB and try
to ascertain what was what. So here's what I've come up with - can +you+
figure out which pin is which?

Board has two outputs, J1 & J2. They are standard 10-pin DIP headers, using
the standard numbering scheme. We'll look at J1; J2 is essentially the
same, but routes to different pins / chips / transistors.

Pin 1 - Col. of 2N3906 (Base is driven by opt. 2 of 1458 - see Pin 7)
Pin 2 - Pin 28 (DB3) of both 1014 & 1015 UARTs
Pin 3 - 1K pull-up to Vcc (12V? Same Vcc as 1458s)
Pin 4 - 150R -> 47R -> Pin 6 w/ XNOR input 1A at 150/47 junction
Pin 5 - n/c
Pin 6 - 47R -> 150R -> Pin 4 w/ XNOR input 1A at 150/47 junction
Pin 7 - 1K2 -> opt. 2 of 1458 (see Pin 1)
Pin 8 - GND
Pin 9 - 1458 opt. 1
Pin 10 - GND

So we have what looks like three (3) each Inputs & Outputs, plus a Vcc and
GNDs:

Inputs - Pin 2, 4, 6
Outputs - Pin 1, 7, 9
Vcc - Pin 3
Gnd - Pin 8, 10

So.. what do +you+ make of it? =)