Need some help: How to find case number of gen Speedie Reduced

[netniet]

I have a gen Omega Speedmaster Reduced ref. no. 3510.50, which I have bought in Februari 1993, and I want to replace the case back, but to order the correct on at Ofrei I need the case number.

Can I find the case number at the inside of the case back, or is there another way to determine the case number (without opening it)

 

I am also looking for a new strap for the watch (lugsize 18MM), will a leather Nato strap look good or will a steel bracelet look better on the watch?

 

Here is a photo of the watch next to my Franken 168000

 

[peterw2]

I don't know about the case back, but here are links to my Instagram shots with different straps:

http://instagram.com/p/g6MWoqCtU1/

http://instagram.com/p/dcyENoCtVX/

One is a distressed leather NATO and the other is a black five ring Zulu strap.

You can decide for yourself. Hope this helps.