RCA produced a series of boards based on the CDP1802 using a common bus built around a 44 pin backplane. I picked up a few of these boards as surplus many years ago. While I have a 10 slot backplane that is suitable, that is a bit much. In the early years it would have required several cards to build a project. CPU, memory, and I/O at a minimum. Now you can get all the memory you can use in a single IC so two extra cards seems to be plenty. The 18S604B cards that I own have a small prototype area which is perfect for adding some SRAM. So three slots seems about right.
The sockets are standard 44 pin PC mount types with 0.156" pin spacing and 0.2" spacing between rows. Some sockets use 0.14" spacing here so be careful. The holes are sized to handle pins requiring up to 0.062" holes. The microboard signal names are on the backside as a handy reference.
The power connector (optional, you can just solder wires into the holes) are for 0.156" spacing Molex type KK connectors.
I uploaded the design to OSHPark and shared it so anyone can order copies. The minimum order is three copies and will cost $42.65 including shipping.