GL1-2xxxxxx is 76
GL1-3xxxxxx is 77
GL1-4xxxxxx is 78
GL1-41xxxxx is 79
Engines have the same series except they have a "E" in them.
GL1E-1xxxxxx is 75
GL1E-2xxxxxx is 76
GL1E-3xxxxxx is 77
GL1E-4xxxxxx is 78
GL1E-41xxxxx is 79
Engines and Frames are NOT Linked. Typically the Serial numbers will be closer at the beginning of the model year and by the end of that years run them may be off by several hundred.
A excerpt from one of the Manuals courtesy of Liam
Matching carb chart is here: http://www.ngwclub.com/forum/viewtopic. ... ef#p453014