Thanks Dave, Rehd, & Severne for the tips.

I think I'll just flatten the prongs or break them off, apply a little dookie schmutz to the flange around the collar, pull them in place with a bolt, (that should make a water-tight seal)and maybe apply a small patch of glass over them. I guess with all that, the prongs aren't necessary! After all, how much twisting pressure am I going to apply with a screwdriver? I, obviously, overlooked the obvious again. Thanks Guys.

Happy Building.

Charles.