I didn't see this in time to act, and probably wouldn't have immediately recognized it, but I've read that Omega released 50 of the ST 105.003. Cal. 321 models in the spring of 1969. The seller indicated it was from 1967. Given the serial of the 321 movement, and the inscription date on the back, is this likely one of the last 50?
http://forums.watchuseek.com/f29/rare-omega-speedmaster-st-105-003-cal-321-a-4212642.html

 

What... £1100??

 

http://speedmaster101.com/105-003/
"105.003
Produced in 1963 to 1965
Although the Omega website states that the last 50 pieces of 105.003’s were delivered in the spring of 1969"
and
"This is the last of the straight lug cases, and were produced over quite a long period. While the case backs show a date stamp of -63, -64, -65, there are confirmed cases of watches released from the factory up to 1969. This reference clearly illustrates the delays some watches experienced between manufacture, shipping and sale."

 

However, I believe the last 321 movement numbers belong to 145.012-68's. If you see a 105.003 with a 26m + movement number, pass.

 

WTF that price has to be a wind up. Movement number wrong or right in parts alone

 

The caseback makes it interesting though. 105.003 caseback, with outer inscription with a date from 1970.

Though could be fake and engraved later but still interesting.

 

Probably 11,000 GBP