That is a straight forward JKF 5513 with a 2813 movement. I just aged the bezel, polished the case a few times and replaced the plexi with a Sternkruz T19. The strap is from CNS watch straps.
Thanks C Master - that gives me plenty to look up.
I found RWI after trying a couple of watches a workmate has; the 2 I liked were his genuine Pelagos 42mm Titanium 2-line (~2015 I think) and Ginault Ocean Master.
I do own a Pelagos 39 homage (the Octopus Kracken titanium version) - nice watch too but it looks a little small compared to his 42mm pelagos on my wrist, so I'm considering going for one of the Pelagos XF V5 ones to start.
Some of the Rolex subs like yours have taken my interest too - though I'm not familiar with the model numbers etc, so having a good browse & read around the forum atm!
John