Quoted from ss-pinball:
What is the title?
Weren't there some early Black Knights that used the remaining System 6 boards before Williams switched?
Yes, all but the mpu board. The power supply changed slightly is really the only difference in the system 6 style version of BK.
I've thought about ways to upgrade the system 6 mpu in the past to support system 7, you could do it with a daughter card that would plug into the cpu socket but that card would have to have an extra PIA on it with a connector to go to the sound board/commas, and extra ram. Likely not worth the design/debug cycle though since you can get Kahout boards again.