tater -
Since it's now sporting the ground balance mod, it's likely the GB pot used is a 10 turn. It could be one with either adjustment end stops, or one of those that will keep turning even after it gets to either end of adjustment range. Those without end stops will keep on turning all day long, but get stiffer at each end of their adjustment range, indicating you've reached the limit. Once you know which type it is by turning it to each end of travel and counting the turns, try to get it to about the middle of its range; for example, from one end of a 10 turn pot, you go back the other way 5 turns...
Once around the middle of the GB pot's range, take a look at the Vaquero user manual on Tesoro's website. You can pretty much follow instructions for ground balancing the Vaquero, taking into account the the Vaquero uses a 3-3/4 turn pot, and yours has....10? It's actually much better off with a 10 turn pot, if that's what was used.
Guessing that a toggle switch may have been fitted for the all-metal / pinpoint function..? Assuming it still has some way to easily go into all metal, that's the mode you want for ground balancing. Again, follow instructions for ground balancing the Vaquero, but get into all metal first. If for some reason the one who modded it did not put a switch in for AM / pinpoint (and GB adjustment), you'll need to do the GB in disc mode...which is a little tougher, but possible. You'll actually want to "power balance" in disc mode for max depth...but that's for a bit later on.
A GB modded Cibola should be a smooth running, deep machine. As a few people have noted about the Cibola, it runs a bit "smoother" than the Vaquero and a 10 turn pot will allow for easier and more precise balancing. I still haven't made time to mod my own Cibola, but I do already have the parts to do it. One of these days I'll get 'round to it...