CBS Studio 54 was the Cort Theatre, which the network leased from the Shubert Organization for Merv after he rejected Studio 52. As far as I know his was the only show to originate from 54. The theatre reverted back to being a legit playhouse in 1972 and it remains one today.
CBS Studio 51 was another theatre, the Maxine Elliott, on West 39th St. Ed Sullivan's "Toast of the Town" came from there as well as lots of game shows. It was demolished in 1960.
I'm not aware of any CBS Studio 53 in NY.