Sportster and Buell are unit construction, lower end and trans in same housing. (not counting latest Buells that will have Rotax engine)
Big Twins have trans seperate, but joined to engine by chaincase. Used to be they had a frame downtube going between engine and trans, but now most models dont, so they look a bit more like unit constriction, a bit harder to tell.
Big twins used to have one cam and the pushrods per cylinder form a narrow V.. the pushrod lines sort of run to the crank centre.
But...
now they have twin cams, so the pushrods are more parallel.
Sportster have 4 cams, so pushrods are further apart and fairly parallel per cylinder.