I won an auction the other day on a very similar (yours is nicer) Sinn 7751. I like the lugs on your watch / the one Im supposed to be getting is a little more bog standard.
...original strap and in my experience this is a generally good predictor that the watch will be in good condition, which it appears to be.
My plan is fit a nice NATO on the watch and use it as my daily for the sumner. These "grand" complications are a pleasure when kept running...
Beg pardon: do you have an idea in your head for FMV (fair mkt $) for these watches? This will be my first Sinn and I plan on keeping it. I think I did OK but I'm not loaded like most of these guys around here...
Since I have such slender wrists - the reason I made those straps for myself - I only have one keeper, which is fixed.
I could add a floating keeper too, but I find it unecessary, since the tail of the strap does not show on the other side.
I use the same "trick" with custom straps -which is to go like +.075mm more than the lug width (only if seems appropriate for the watch head). Very subjective and not scientific !! Lulzz