On Saturday evening I had time to securely fit the sockets and wire everything up. I'd have felt more confident if I actually knew what I was doing; my knowledge of electrical circuits being nil, there was every possibility that some disastrous short or otherwise bad connection would result in the whole thing blowing up. However, dumbly following a plan and reinstating the ground-away traces with jumper wire, I ended up with two secure DIN connectors. The power connector is especially sturdy, being held in place both by hot glue, and by the pins soldered to the remains of the traces underneath the board.

At least to top side of the mainboard looks pretty damned neat:

And - to my absolute delight - it even works:

So the next job is the VBXE board, followed by the new PBI connector once the solder-cup Centronics 50 connector arrives from RS.