Okay, new KBCC came home this week, plugged-it in, worked better than the previous one, even though the KBMM is of the earlier model (with through-board ICs rather than SMT ones (smt = surface mount).
I tested it on the same motor; motor's really fine and runs very smooth.
Next step: do not blow it...

I machined a coupler to join the servo-tek DC tach to the motor; mounted the tach and gave it a spin (without connecting it to the KBCC). Not only does the motor runs smooth, with the KBCC's help it runs steady (without load).
I hooked the tach's wires to my multimeter, and gave the motor a go; at full speed I get 35.6V from the DC tach; this in turn leads to a nice 5085RPMs

Following the math on the KBCC manual, I get a value of 28906 ohms for the tach resistor; in the 5% resistors world, this leads to a 30000 ohms.
My former KBMM board didn't have a J1 jumper wire (there was a set of holes where standard jumper pins could be installed on the board, but nothing connected to them). My new one does have a 20-ga (or so) wire. Did you have to cut a wire on your board to enable the DC tach?
On the other hand, I used alligator clips to connect to the APRM relay's coil pins. The relay has around 110VDC between coil pins and activates my 2 SPDT relays (couldn't find DPDT 110VDC relays locally so I "created" a DPDT from 2 parallel SPDT relays...) I'll use these to reverse the relay's polarity.
I'll try to locate some terminals that could be used instead of alligator clips, else I'll build terminals myself out of thin brass sheet. There are 2 designs I'm thinking about; either "j" shaped terminals that'll slip over the flat pins on the relay (and hopefully lock in place) , or spring-clamp style. I'll let you know about these when I'll get there.