The early Treks were also available as framesets only, so they were often built up at the LBS according to owner's preference. Also, it's my understanding that custom details could be ordered (eyelets, tubing changes, braze-ons) directly from the factory. I'm not sure geometry could be changed, however.

Or, as EjustE postulates, the braze-ons were added later. Is the frame a light metallic blue? I've got a '78 TX 500, but no mid-fork braze-ons.