For those of you who've asked, I've been away in Hong Kong and Melbourne. Pleased to say though that the watch collection now has three more additions: a neat 6309-7040, a 6118-8000, and something Swiss.
Here is the noticibly larger -7040 (built July 1984) against my older everyday rat-729A (built October 1986):
While the case is obviously larger, the dial and bezel appear to be the same size. Comparing them though, the bezel on the -7040 is about 0.5mm larger - I always thought them the same.
Apart from case dimensions, the most obvious differences are the face markings:
The bezel and 'Seiko' fonts appear the same, as do the hands.
The crown protectors:
Dial details though vary:
-7040 says '6309-704X T MOV'T AND DIAL JAPAN CASED HONG KONG'.
Case back, with same tsunami, but obvious case shape difference:
Again case shape and crown protector variations visible (the -729A looks as if the crown protection could take someone's eye out):
After a few minutes under the photo lamps, the difference in their lumescence can be seen (note earlier watch's decay and lack of hour markers in the dark):
The -7040 will remain a collector item and the -729A the everyday biking and skiing device.
(Hopefully, I'll be able and post the results of another Tokyo watchshop adventure soon too. Thanks for the appreciative comments.)
and late versions of the 6309. I had read in posts by Shawn and Kevin Chan that the 729A case was similar (or same ?) as the current SKX-xxx divers. Your pics clearly show this. Welcome back. Looking forward to another of your Tokyo watch shop tours.