A very good illustration of why no one should use catalogs like this as a reference...practically everything in the description is wrong.
No Ketland gun predates approximately 1759/60 and examples that may fit in that time frame are extremely rare.
William K went into business under his own name in 1801...no "WK" marked gun predates that.
The skeleton side plate shown was in use well past 1800...it was an earlier sty\le that continued on for export guns long after it was "old fashioned" at home.
I won't go on boring the readers but I've seen the Rifle Shoppe catalog cited as a reference many times. It is isn't...