Hi Paul,
I recall you having those problems with your castings. I wouldn't recommend going to a larger pin. I still use the old system of upper and lower pins. I once lost the upper pin at Spirit Lake, and the rudder turned and bent the remaining lower pin at an almost 90 degree angle. Ouch!
I must say though, that had the pin been a lot stronger, it may well have ripped one of the gudgeons right out of the transom, a much more expensive repair for sure!
Also, if you ream it out, how are you going to use your bushings?
Good luck,
Tim J.