The original 1950 production had a full Overture followed by the "Runyonland" ballet. The movie does a shorter overture with the Main titles and then goes into the ballet.
Decca's original cast album drops the Overture and records only a shortened version of Runyonland to lead into the Fugue for Tinhorns (remember in 1950 they were still recording on 3 1/2 minute 78 RPM discs.)
RCA's disc of the 1992 revival has new rchestrations and devotes the first minute and a half to the new overture and then has a one minute excerpt from Runyonland (it was longer in the stage performance!)
JAY has a 2-CD set using the original orchstrations and as far as I knw that is the only place where you get the full original overture (for 4:02) and the complete Runyonland ballet (3:31.)
Most modern performances cut the Overture since it's long and not one of the best of its kind. But two recent community stagings that I covered used the full overture so it is part of the current available score.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com