I guess this is what commonly known as Watchco Omega SM300 (by the Australian if i'm not mistaken) since it's restored by them using all authentic Omega parts...don't really know where they got those parts from, directly from Omega?
The non-watchco SM300 in mint condition is really hard to come by, the most sort after is the "T" dial (not the lumi), there is a "T" (with circle) on top of the "Seamaster" printed on dial...
I once owned this watch (exactly the same as Andy's one
) before and with 2 original bracelets but let go due to some reason...
There is no serial number on the case but there is a serial number on the movement itself
This movement is Omega in-house movement in the early day which no longer in production... if i'm not mistaken, it's Cal552 for no date and Cal553 with date....both are unadjusted but I have to say that the one i owned was very accurate, i timed it before and it's gain +5 sec daily consistently over for few weeks
as mentioned by Andy, there are a lot fake out there, so if you interested to get one, better do some homework and usually hard to come by in any used store
Before i got the real one i actually bought a fake one on the Bay (300GBP, too good to be true, haahah) while i was staying in UK :p Then i sell it back (where it come where it go) with the same price i bought and clearly stated the case, bezel, dial is after-market.... luckily some one bought it to reduce my damage :p
Cheers!
scott