The original "GM" key blanks are still available. In this era here are 8 different key series that vary by model year and whether the lock is
ignition or door / trunk / glovebox. They will be common with other GM vehicles and the series is identified by an alphabet letter stamped on the
side of the blank;
'73 ignition - "E"
'73 door - "H"
'74 ignition - "J"
'74 door - "K"
'75 igntion - "A"
'75 door - "B"
'76 ignition - "C"
'76 door - "D"
'77 ignition - "E"
'77 door - "H"
'78 ignition - "J"
'78 door - "K"
If your locks have ever been changed all bets are off. Also I have seen a few transmode coaches titled later than the chassis i.e. a "78 Royale"
based on a '77 chassis. The VIN defines chassis year "TZE16XV100001" where the "X" is the model year.
One last tip - take good clear digital pictures of your keys. A good locksmith can make duplicates from photos.
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Chris Geils - Twin Cities
1978 26' Kingsley w/ very few mods; Headers, Progressive Dynamics 9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, 50k mi