Help identifying vintage Omega with radium dial - serial 7,7

Hello everyone,

I would appreciate some help identifying this vintage Omega from the attached photos.
The manual-wind movement is marked:
OMEGA Watch Co Swiss
17 jewels
Adjusted two positions
Serial number appears to be 7,7milion
The watch has a radium-lumed dial, small seconds at 6, luminous Arabic numerals at 12/3/9, a signed Omega crown, and a caseback marked only “STAINLESS STEEL - WATERPROOF.” but execution looks sketchy. I cannot see an Omega signature or reference number inside the caseback.
Could anyone help with the following?
What is the movement caliber and approximate production year?
Is this dial, hands and case combination correct for the movement?
Does the dial look original, restored or completely refinished?
Could this be a legitimate locally cased Omega, or is it probably a later recase?
Does the radium lume appear original, and are the hands period-correct?
Is it possible to identify the original reference or model?
What would be a reasonable market value in its present condition?
The 7.7-million serial seems early. I am primarily interested in understanding its history and originality, but a rough valuation would also be very helpful.
Thank you in advance for any information.

I compared the movement with this base 26.5 SOB example.

The overall architecture and finishing look very similar. What particularly caught my attention is the winding click: mine appears to have the earlier angular pawl engaging the large ratchet wheel, like the base 26.5 SOB. Most T1 and T2 examples I have found use the later round click. I did find one movement described as a T1 with an angular click, although it may have been misidentified.

Could my movement therefore be the original 26.5 SOB rather than a T1 or T2?

As I understand it, these were successive iterations of the same movement family:

• 26.5 SOB - introduced circa 1926
• 26.5 SOB T1 - introduced circa 1932
• 26.5 SOB T2 - introduced circa 1933

Unfortunately, because of the radium dial, I would prefer not to dismantle the watch further to locate the caliber stamp without suitable controlled conditions. Am I interpreting the click design and development sequence correctly?