This is (rather "was") a sample or prototype plate which may not have ever been released for actual use.

This a "FARM EQUIPMENT DEALER" plate, and this category may have been absorbed into the "NON-CONVENTIONAL DEALER" type that is used today.

This particular plate (or at least part of it) continues its life as an ashtray,
and is the only specimen I have ever seen of this type.

Many thanks to John Willard - ALPCA #909 - for letting me know about the existence of this type
and for sending me this picture.

I superimposed this over a standard 1960 dealer plate.
This is what the actual plate may have looked like:

... but don't take my word for it !!