If I were you I would just get a Davis megalight.
Mega Light™ Utility by Davis
Hang it above your bimini from the backstay or topping lift.
In close quarters or crowded areas an anchor light is going to be more easily seen if it's lower to the deck. Plus, it's a pain in the butt to have to climb the mast when the bulb burns out or the contacts get corroded and the light stops working. Which seems to happen often with lights at the top of the mast.
Keep it simple. Keep it cheap.