I had some unattached QBUS backplanes laying around and I started to put random CPU's and cards in them. I used some simple caged power supplies to generate the required +5V and +12V (MeanWell RS-50-5, MeanWell NES-100-12).
I quickly realized that nothing would boot without something to wiggle the DCOK signal. And, I needed a 60Hz clock.
I found a simple PIC circuit created by John Wilson and made a simple 2 layer PCB. I added some LED's and push buttons and them wrote some new code to generate reset, halt and the line clock.
Initially I made 4 of these and found they work great. I've made another batch of 10x with a current cost of $30 each.
One button resets the system. The other drops into the debugger. The led's show power and run state. Simple, but does the job!
This is how it looks when installed:
heeltoe.com