Mine are stand alone. Aluminum,shaped right and welded to the mast. a halyard from the underside, out near the tip and a deck light on the underside, with the wiring inside.
When I got this boat it had an aluminum mast that was too short and had shrouds that cut through the passageway, so one would have to duck, or get a shroud across the neck. I replaced it all, saving the spreaders for the new mast. I had a taller mast made up out of pipe, lengthened the lifting boom so it would reach out over the water to the side, and mounted it without shrouds. I moved the base down a deck and attached the mast to the flybridge deck for support. That allowed me to use it to lift stuff, including a Laser that I carried for several years, and clearing the passageway eliminated the threat of injury while going up or down the steps. Aluminum pipe is strong enough and flexible enough for the job, without shrouds. When lifting anything heavy, I tie off from the spreader bases to a forward grab, just as belt and suspenders.
Find yourself a shop that will weld Aluminum and get it done right. You will never look back.