Help with a project please
I'm disassembling a Mercruiser Alpha 1 Gen 2 outdrive on a boat. The hinge pin on the port (left) side of the gimbal ring that goes into the bell housing is seized. The bolt is made of stainless steel, the bell housing is cast aluminum. It is a female flush mount bolt with 12-point teeth. The teeth were stripped out so there was no way to remove it. I have drilled out the bolt with a 1/2" bit all the way through. However, the bolt is a little larger than 1/2" so there is still material left.
I was wondering what you would recommend to get the remaining material out. A reamer? If so, what kind? A larger drill bit? I'd like to salvage the bell housing if possible, but I'm worried the threads are already ruined if the stainless steel and aluminum corroded together. Everything is still on the boat so I'm doing the drilling with a handheld drill. There is nothing critical here, just a project boat I'm restoring.
Pictures for reference: https://imgur.com/a/iUXtGnl
Thanks for any help.