50 years ago that may well have been built with polyester, not epoxy. I'd definitely grind as much as I could and perhaps use judicious heat to help...
Keep in mind that an internal patch may keep water out of the boat, but it won't keep water out of the surrounding wood. If you want to save as much...
I just had my 2nd total knee replacement. At 75 I probably won't need to worry about the 15 year rule...but my Mom made it to 97, so ya never know. ...