I've finished the modifications to all eight relay boards finally, namely jumpering all the relay poles together and changing the 10 pin header from straight to right angle. I think the next step will be to build a control board, test it and repeat for a total of four. The control board holds 2 shift registers and a pin header for each which will connect to its relay board.
In the midst of thinking through the above, I am also pondering the chassis layout. Maybe a plywood base and an aluminum cover with access doors to the relay terminals - design pics coming at some point.