Here's the whole gatefold spread of it, which now I think of it, was used in full on the billboard - logically, enough, given that billboards are oblong not square.
Wish Wishbone Ash's music were teensy bit more exciting... the twin lead guitar thing is pleasing and moderately dynamic (although not as driving and low-slung as Thin Lizzy's). The archetypal second-on-the-bill Brits-in-America stadium act, said someone (Carducci?). They've got a sound that's just distinctive enough. Argus is considered the (minor) classic.
Packaging-wise these gatefolds are also nice.
But this next one is yer classic mid-to-late 70s mainstream rock album cover, where the Hygnosis-type visual joke / saucy pun (see also UFO's Force It) is going off the boil, Most likely matching the contents of the record too.