I laced a SA 3 speed hub to a set of 27" alloys and used "plastic" fenders. Bike rides great. No mods required except homemade "extenders" on the fender stays and I found white walls which to my knowledge are unavailable in the Schwinn size 26" rubber

The alloys lighten it up a bit though it's still no lightweight but once you get it rolling on the flats or down hill it's fun to ride. I have a stock Racer with the 26" wheels and it is much less agile.

And just for the record, I'm about to take a Speedster or Racer, I don't remember which cause I repainted it, to which I laced a 2 speed Bendix kickback hub out for it's maiden run. That rear hub is heavy but we shall see how it rides.