Well, the passenger side is, but the drivers side is way wider than the tabs on the 340.
But, I just found some 318 brackets on ebay so I'll have to modify the drivers side to fit once I have them.
Don’t know if possible in your case, but I would be inclined to modify just my own single 273 mount, rather than buying a pair of 318 mounts, and still having to modify one side anyway.