Simplicity 5511 vintage sewing pattern, dated 1964.

Jiffy One Piece Dress: 

Shift dress features a scooped neckline.The sleeveless dress has front diagonal darts and a back zipper closing.A self fabric tie belt may be worn Empire style with chain loop carriers at side seams; or at waistline, an optional belt is worn (purchased or self fabric) 

Size   16:

Bust   36 inches / 91 cm

Waist 28 inches / 71 cm

Hip     38 inches / 97 cm

Pattern is unprinted, perforated with symbols and factory folded. Envelope has shelf wear, small hole in one corner, store stamp on the front.

More '60s patterns here:

http://allthepreciousthings.com/collections/1960s