You've got limitless cash, no bribery's. Foster isn't any better then he was. Your job is to make him as much money and prestige as plausible and you can dip him in any era from 1930s onwards. He cannot fight in a weight lower then he did. If he can make CW he still fights at HW for example.
I would certainly put him in there with Billy Conn, just to showcase his superior power against a popular fighter, and then go for the Calzaghe fight
Current era, do everything in my power to get the Ruiz spot against Joshua. Foster goes on to get a rematch against Joshua for a bunch of money in the middle east, then he can get another cashout against Fury