just did this....
I just did the same job on my '78 Hunter 30. If your handrails are varnished, make sure you use a heat gun to remove the varnish surrounding the teak plugs, or they'll take out some of the surrounding teak from the rails when you remove the plugs. Once the varnish on the plugs is gone, they're easy to remove with a drill, but be careful not to drill into the underlying screw head.The handrails on the H30s are not throughbolted. They're simply screwed into the deck. This means there's a hole through the fiberglass deck, through which water can enter the plywood core of the deck. Water BAD!! When the handrails are off the boat, drill the screwholes oversize (about 1") and fill them with epoxy. After the epoxy sets, you can redrill the screw holes and mount the handrails into solid epoxy with no way for water to enter the plywood core.