I assumed the buckle and strap were fake (I'm not up to speed on modern straps etc).
If the box, strap and buckle are genuine then this will certainly increase the value of the package.
I maintain that head only, a gold plated Seamaster Cosmic isn't selling for significantly more than £250 in a private as-is sale, which is how things are usually priced here.
Unless things have moved significantly, I don't see $400-500 being the mean auction price for these head only in steel either but perhaps I'm basing it on 2019 pricing.