After the Beastie Boys released Paul's Boutique, they wanted to spend a serious amount of time getting instrumental before their next album.
Their manager at the time recalls Ad-Rock getting outfitted for his guitar at Westwood Music. Apparently, Ad-Rock wanted a guitar with a finish like the one Bob Marley had- consideration of tone wasn't the primary motivation for selection.
At the time of the release of Check Your Head, not many people realized that the Beastie Boys actually knew how to play instruments before they started rapping. The cover of Check York Head (taken by famed photographer Glen Friedman) is supposed to evoke an instrument-armed Beastie Boys version of the Minor Threat Salad Days cover (which Friedman also shot).

