One difference between the M17 and M37 is that Ithaca added an extractor to the top of the bolt. Early Ithacas in some of the the early runs of the first year didn't have the top extractor.
Whether there were problems without the extractor on top, I dunno, but Ithaca didn't make the 20 gauge in the first year, only 12 gauges. Despite the cut stock, the gun you are considering is a desirable one and would make a fine dove gun. In that the stock has been cut, I wouldn't hesitate opening up the barrel should you desire.
Do you still have the 28 gauge M12 or do you kick yourself in the butt for not having it? wink As you no doubt know, that one is at the top of the heap in both value and desirability.