Using a bunch of spear wire from a old central Locking kit, I have tested the Encoder for player 1. It works fine though the number lock is activated as indicated by the led on the encoder pcb.
I probably will not used the current setup of buttons and may have to rewire the buttons that I daisy chained as they are using the same control wire on one side of the switch.
A friend of mine has a spare control panel that I could have done with to keep things neat, but a planned visit to see him did not happen.
My next step is to wire up a second set of buttons and a joystick for player 2 and make sure I can get them both working from the one keyboard controller on Retropie.
A friend of mine told me that the Pi 3B+ does not like having 2 keyboard controller connected and that the Bluetooth Keyboard I was intending on using for non programmed functions on the final machine, may conflict!
I will test this at some point, but if it is a issue I have the option of setting things up by SHH protocol over the network.