As someone suggested, it is possible to repair with fasteners and JB Weld (which is metal-filled epoxy). But doing that is like trying to polish excrement. Unfilled Delrin was a stupid material to use for the application in replacement of steel or aluminum. At least the carbon fiber matrices from present day have the carbon providing tensile strength (and that's a dumb-ass idea as well).

IMO the better bet is to replace Simplex with SunTour/Shimano/Campagnolo, even if doing so makes your bike period incorrect.

And if you must replace with Simplex, make sure you are using one of the Super LJ all-metal ones.