I don't know this, but as a guess RH should stand for "reflex horn" (e.g. like the original Sunn 2x15 cabs, as well as Musicman 115RH or 212RH which are essemntially the same design, but the size of the Sunn cabs). Basically it would be a rearl oaded horn (you can see the drive units, and there is some direct radiation of sound) and the horn isn't a full proper horn. There is na large than usual compression chamber behind the driver, like a ported box size, with a rather small/narrow horn throat; a bit of a ported/horn hybrid.
"SH" I would guess stands for "scoop horn." That would be either a front or rear loaded horn but with a proper curved (usually concave, but could be convex) scoop style horn; think Jamaican sound system.
