I am looking at buying that same model locally (Mercury 6508) so I also have questions. I went to look at it today and confirmed that it accepts standard tooling. Regarding tooling, I have received lots of help from the folks at http://www.powerbrakedies.com/
The particular press brake I am looking at says 10' x 10 gauge on its nameplate. It doesn't say how many tons it produces at the bottom of its stroke, but 10' x 10 gauge might imply 85 tons. (look at the tonnage chart on the site above or on other sites on the web). I'd sure like to know for sure though. I've tried to find a link to the original manufacturer but cannot. I thought at first that the model number (6508) might indicate 65 tons, but as I came across other mercury presses and saw their model numbers I realized that there is not a direct relationship. The strangest thing about the local press brake is that it has a 2' long horn on one side. It is really a 12' wide press, although it is listed as a 10' press normally. I've come across this in other listings for Mercury presses. The horn is not really an add-on - it is part of the casting but it is outside the two large cylinders that hold the upper ram. Very strange. It would let you get in to do some tight work on boxes, perhaps, as it is outside of the housing.
Please let me know as you learn more about your press. I'll do the same. I am close to buying this one.