Trying to replace the water pump on my 1966 Merc 500

I just recieved this boat from a relative, and I just finally got it running. While running I noticed no water coming from the tattle tale. So I figured the impeller needed replaced so I drained the fluid from the lower unit and proceeded to remove the bolts that hold it on but when I tried to remove the nut that holds the trim plate on I cant seem to get the right socket or any socket for that matter down inside the hole. The only thing I can get down there is a allen wrench. Is there somthing I'm missing?? The diameter of the hole is about 1/4 in. if that. A little bigger than the diameter of a No.2 pencil. If anyone has any info I would greatly appreciate it. As of right now I'm at a stand still until i figure something out.

Thanks in advance, Dustin

Re: Trying to replace the water pump on my 1966 Merc 500

This has been talked about the last couple of days, it's either an allen or 12 point, shine a light down inside and have a peek.