You don't say how long it's been setting but I assume it's been awhile. When I bought my '52 1/2-ton it had been sitting for years. I replaced brake lines, master, wheel cylinders... everything! Make sure the bleeders aren't clogged, make sure the lines aren't rusted shut (brake fluid draws moisture.) Pull a brake line off a wheel cyl and see if you have fluid there.
You don't have a lot of room for error if it is all original... I wouldn't want to take a chance with old parts.
Jim
