Grid: quarter-hour; meta: 5 extra 

Matt Gaffney’s Wall Street Journal contest crossword, “What Should I Where?” — Conrad’s writeup.

This week we’re on the lookout for a four-letter a part of the physique. There had been 4 numbered theme entries, every containing a chunk of clothes:

• [17a: 1989 World Series MVP who also pitched a no-hitter in 1990 (1)]:  DAVESTEWART
• [11d:Eponym of an Australian island (2)]: ABELTASMAN
• [57a: “The Ten Commandments” and “Ben-Hur” co-star (3)]: MARTHASCOTT
• [28d: Whose Line Is It Anyway?” host since 2013 (4)]: AISHATYLER

Those 4 items of clothes matched a grid entry containing a physique half as soon as one letter was modified:

• VEST -> CHEST-> CHES(S)
• BELT -> WAIST -> W(H)IST
• ASCOTT -> NECK -> N(O)CK
• HAT -> HEAD -> HE(E)D

The modified letters spell SHOE, resulting in FOOT, our contest resolution.