Kevin,
My manual states that the x3 series tractors had 38, 42C, and 42M two bladed decks, and in both a three blade 48 inch and 54 inch cut deck sizes as well...housings of course are larger in dimension. I don't recall if the three bladed decks were ever offered on the smallest tractor in the series, the x300.
None are timed. I sent you an excerpt with some info about these decks...
Chuck