Matching Wheels to Trucks and Deck

Hey all, I want to create a cruiser setup from an old 8.5" popsicle. Currently I have some indy 139 (8" axle) and a thunder 149 (8.5" axle). I am looking at getting some fatty hawgs, but I'm worried the wheels will add some extra width, causing it to poke out. How do I even figure out how much width the wheels are going to add to the trucks?