I was looking at a GB 36 that had tanks that needed to be replaced. I was thinking about buying and doing a major refit. In my research I came across John at Oxfords Yachts in Maryland. He’s a Grand Banks specialist and is a wealth of knowledge, and a very nice guy. He has also made a bunch of YouTube videos
https://oya.com/boat-repairs-and-mai...ks-fuel-tanks/
Good luck with the project
S