Can you name an episode where all 4 were acting?
I dont know how to embed YouTube videos, but here's a link: http://www.youtube.com/embed/Sk4ujI-EOMk
FROM WIKIPEDIA: Donning a full head of hair, Curly made a brief cameo appearance (doing his barking-dog routine) in the third film after brother Shemp returned to the trio, "Hold That Lion!". It was the only film that featured Larry Fine and all three Howard brothers, Moe, Shemp and Curly, simultaneously
; director Jules White later said he spontaneously staged the bit during Curly's impromptu visit to the soundstage.
That's the one! It was pretty wild to see him with the full head of hair. I remember reading years ago that he had the small cameo and I saw the episode last year with my son. I know I'd seen it several times before but never thought it was curly.