The La-Da singer (as opposed to the La-La singer heard on the record album - an alternate take) and the trowel were originally heard in the DL Mansion. They were both removed from DL sometime in the late 70s(?). The La-Da singer continued to be heard in the WDW Mansion until just recently when they replaced almost all the vocals there and it was dropped. The trowel sound was added at WDW at that time (so I've been told).
It is believed the La-Da singer's vocal came from the "Captain" just to the right of the hearse. (Dressed like the Gorton's Fisherman.)
BTW - the Opera singers, Headless Knight, Executioner, and Gus the Prisoner mix near the end came from my own audio ride-through mixes.