As absinth said check the chassis number there are a few ways to check original body or body parts for hz
Cut outs in stone tray for spoiler spoiler was standard on hz sandman
Black door handles
Black outs over original paint around doors ,sills ,beaver etc
Evidence of decal or paint variation inside lip of guards and door etc
Off coarse double head light front end
Full length head lining comby thing
Tyre placard number on clove box
I know these things can be changed individually but the more off them you have points to sandman body