Vintage Seamaster Identification

[J_Suth]

Hi there,

Here is a watch I inherited from my father. It is clearly in dire need of restoration.

I'd be interested if one of you could help identify what model of Seamaster this is? Also, what the 'IS' on the left hand side of the face means? I have not seen this elsewhere.

Thanks in advance for your help!

 

[efauser]

What are the numbers inside the case back?

 

[X350 XJR]

J_Suth

what the 'IS' on the left hand side of the face means

This is likely a corporate logo of some sort.

Photos of the case back, inside and out would help.