Easy to check this. Look at how much clearance there is from the top of the tire to the crown of the fork. Now, imagine the tire moving 3" - 4" up. Would it ram the bottom of the fork crown?

If yes, then adding an 80mm fork would slow your handling down, and make steep climbing difficult. If you ride bike paths and dirt roads and you aren't particularly aggressive, it might be okay. If you like tight singletrack and climbing, forget it.