On my installation(s) I used both the gasket supplied with the adaptor plate as well as the gasket that came with the pump. As for the sealer, I prefer a light coating of #2 Permatex on both side of the gaskets and if you have room between the fan and radiator I would use 3/8 studs in the holes you threaded in the block. If you don't have sufficient fan/radiator clearance to slide the pump/adaptor plate over the studs, I would use bolts with some anti-seize. Having to pull the radiator to change out a pump/belt would be counter-productive.
If you use studs, I'd use thread lock in both the holes you tapped and you might find that you could use the stud as a mounting point for your alternator/generator bracket.
Dave
