Most of the good wee heavies seem to follow the Traquair clone route, which is a good thing. 99% base malt (Golden Promise preferably, or Marris Otter), and 1% Roast Barley, then kettle caramelize the hell out of 1 gal of 1st runnings. Bittering hops only (EK Goldings, Fuggles or N Brewer) to style.
And for what it's worth, Skull Splitter is just one of Orkney Brewing's fine offerings. Try Red MacGregor, or Dark Island.