Re: 1/6 RDR2 Arthur Morgan
I think for things like this you are always best basing it on the promo art/default look, because in game these the characters' clothing, head and facial hair, and even weapons colours and styles are so customisable that to try to base them on anything else will just lead to headaches and complaints. Best off sticking to the default and people can customise theirs however they like after the fact. Just be sure to stock him up with a nice range of weapons options. I'd suggest a pair of revolvers, a sawn off (or two), a shotgun (pump action or double barrel), a repeater rifle, a bow, and a knife. There are plenty of other options you could add, if you wanted to, on top of that, like dynamite or throwing knives or a tomahawk or other guns.
For the record I'd buy good quality Arthur Morgan and John Marston figures in a heartbeat. I'd also buy an 'undead nightmare' variant of John Martson, if it ever happened, as well.