Reference: ST 176.0009

It is model 176.0009
Here's info from the Omega archive site (free registration click here ).

Speedmaster - Mark IV Gents' leather strap
Reference: ST 176.0009
International collection: 1973
Movement
* Type: Automatic (mechanical)
* Caliber number: 1040
* Created in 1970 22 jewels
Functions: Date, Tachymeter, 24 hours, Chronograph
Case:Stainless steel
Case back: Screw-in. Full metal.
Dial: Matte black, with luminous hour markers and white luminous hands.
Crystal: Mineral (flat)
Bracelet: Leather
Water resistance: 50 meters
This watch may have existed with different dials.
More product information:
Case : "barrel" shape (14,9 x 41,5 x 45 mm)
Size between case lugs : 22 mm Bezel : with inside tachometer "0-60" scale International Collection : 1973-1977
Swiss retail price (1973) : CHF 650.-
Also available on SS bracelet of ref. ST 1162/172
Later replaced by ref. ST 176.0012 JLM