by "it's run" I take it to mean that it was some form of stage presentation.
Yes. Healy was a headliner in vaudeville, and later in touring/Broadway stage revues.
But Moe absent for a year and a half?
Moe retired from show business in 1927, and returned in early 1929.
Larry absent for a year and a half?
No, I did not say that. Larry left after A NIGHT IN SPAIN to go on his own. He and Healy lost touch for a while, and Sanborn was brought in to fill the spot.
Moe was coaxed back and joined Shemp and Freddie for rehearsals of A NIGHT IN VENICE. After a brief absence Larry eventually got in touch with Healy, and was brought back in before the show opened. Sanborn remained a Healy stooge, but a fourth wheel.
And by "4th wheel" do you mean that Sanborn was not part of the eye-poking stuff, rather just a regular cast filler? The photo of him posing apart from the other 3 implies that.
Yes. He had his own act, comedy xylophonist, just like in SOUP TO NUTS.