From Jason S
'73 had smaller rollers (note: some early 1974's had smaller rollers, check)
74-87 have the same size rollers, but the shaft the handle attaches to is different length.
73-76 had the same handle shaft length.
77-87 was a longer handle shaft.
Here is a photo comparison of the 74-76 (74 K-10) on the right and the 77-87 on the left (83 C-10).
Handle shaft length:
Overall dimensions:
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