The guide rails on a Smith machine are precision-machined and vary a lot between brands, so working from your model's manual matters more here than on most gym equipment.
Pro tip: Photograph the bar hook positions and rail spacing before disassembly, Smith machine geometry varies enough between brands that a generic guide will not match yours.
Watch out: Do not attempt to lift the assembled frame with the bar still attached and unsecured, an unlocked bar sliding down the rails at the wrong moment can injure hands or feet.