Whether a triplizer will work or not depends on your bolt circle. 52-42 cranks often had a 144mm 5-bolt circle, and triplizers for these do exist, although there aren't tons of them floating around. You'd also potentially need to change your BB spindle to push the drive-side crank a bit farther outboard.
Alternately, you could just buy a triple.
Originally Posted by
bikemig
There are lots and lots of old MTB triples out there with 110/74 bcd chainrings. Find one you like and run it as a double.
If you're going to run a triple as a double using the small-middle positions on a friction setup, I don't understand why you wouldn't just run it as a triple. Using it as a small-middle double doesn't get you any benefit in q-factor, and the bigger shift will be less smooth and more disruptive, not to mention that you'll likely end up with less total gear range. Seems like the worst of all worlds.
Well, except for the design of that Super Record rear derailleur, I guess. It's not designed to play well with wide front gearing, either in terms of geometry or chain wrap. Personally, I'd ditch it and use something like a SunTour GT derailleur.