Your SERIAL # EN510423 (May 1977 SUBURBAN ten speed) should have the new Shimano FFS (forward freewheel system) on the one-piece Ashtabula crank.
What is interesting is that for some color choices (SKY BLUE) Schwinn chose to keep the Traditional Style DECAL, where in other colors, you have that "MODERN-NEW" style on some colors.
Schwinn Lightweight Data Book (Detail 1975-1979)
1975
https://waterfordbikes.com/SchwinnCa...0/1975_15.html
1976
https://waterfordbikes.com/SchwinnCa...0/1976_15.html
1977
https://waterfordbikes.org/SchwinnCa...0/1977_10.html
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I believe that those REFLECTORS that are there on your bike are correct. Schwinn built it with those at that time.