Put some heat on the bolts, they are probably loktited in place.

Not too much heat though!

I've only done this for chinook uj's, so don't know how prolimit works.

Is the screw that goes into the board the same one that goes into the UJ?

If so then you may have to use two nuts on that thread.
If not then there will be a way to put a socket or something onto the head of the bolt that goes into the boge joint.

A picture might help to figure out what's required

Worked it out. Heart transplant would have been easier. Pro limit have a moulded base. Needed to drill from side to expose a side Allen key bolt. Surprised they don't leave open but guess it's rush proof. Got all the way then the bloody new boge is wrong size thread. Who would have guessed they made it in several sizes. Will post photos but ultimately by the time I bought lock tight. Boge. Time. A new $70 base prob cheaper. At least I partially won.