Hello vint-mow
I feel I can give you a rough year of production.
This utility base was Palmer's first base but they used about
half-a-dozen engines over its life span - from about 1960-64.

The only ads I have that date this model come from 1964.
I'm guessing that 'L4L' stands for Lawnmower-4-stroke-Kirby-Lauson

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These images from ODK show the decal and badge:-

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[Linked Image]

Hope this helps.
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Jack