Re. Clive - Yes, the picture of the top of the board is particularly bad. Also, agreed with post-in-one-place, but we're here now so let's move onwards.

OP: You have to acknowledge the image is difficult to interpret, but we can deduce the following:-

It's a parallel port interface (the big black 25W connector on the left of the image as viewed). That immediately gives us options in terms of a replacement BoB, if necessary, although the board looks to be rather compact - we can't tell if a replacement board would actually physically fit, but we can play with that with a better photo.

If I take my glasses off, the image swims into... less focus... okay, worth a try. But, I have to admit that the connectivity to the board appears just to be power (lower right) followed by 4-axis drivers (the four four-wire interfaces above that). And NOTHING ELSE?! The circuitry around the lower-right connector I would guess to be a local 5V logic supply for the board (hmmm, maybe... pretty heavy duty if it is), and board silkscreen printing appears to show a power jack (not fitted), some jumpers - not fitted (although there's a two-pin jumper fit, but can't read the silkscreening around that). What isn't evident are the usual 5x digital inputs - used for E-Stop/Probe/X-Limit/Y-Limit/Z-Limit (conventionally, although can be used for practically any function). Nor any suggestion of the usual opto-isolated inputs to support these.

We do need a better image and to understand how much you're prepare to play with this. I'm half guessing (through squinted eyes) that the board does not support additional inputs, as would be required for the limit switches. A cheap Chinese BoB will likely work well (if we can work out the pinouts for compatible connectors to the existing wiring looms), and would cost less than a tenner, and give you a more conventional interface. That would work almost as a plug-and-play swap for the existing board - though you'd have to map the new input(s) through onto Mach3/whatever-you-use. It's an option.

For now though - as much as a buggeration as it is - clear photos would really help.