Creating a shower out of a galvanized tub involves plumbing the tub in the same way as you would a claw tub or any free-standing tub, except that you'll have to drill your own hole or holes if they're not already fabricated. Once you have a hole in the base for draining the water, you can attach the faucets and the overflow pipes to the side. A circular shower curtain is all you need to control the overspray and provide an old-fashioned galvanized tub and shower combination. The directions are vague since each installation is unique to the tub and the home.
Purchase the drain and overflow pipe assembly. Mark the positions of the drains on the galvanized tub with a pencil and cut them out using a metal hole bit on your electric drill.
Attach the gaskets and the drain/overflow pipe assembly according to the manufacturer's directions.
Purchase the faucet assembly with the shower attachment for a tub installation. Decide where on the tub you want your faucets, and cut the holes to match the requirements of the faucets, again using a properly sized metal hole-boring bit. File the edges of the hole to smooth out any rough areas.
Attach the faucets to the side of the tub and connect the water supply hoses to the faucets, following the manufacturer's directions.
Connect the pipes to the existing drain pipes and water supply in the bathroom, using the help of a licensed plumber.
Install a circular shower curtain rod around the top of the tub, either from the wall or by suspending it from the ceiling. Hang the shower curtain on the rod.