Mine is a '78 Newport 30 MK II. The fuel tank is located starboard rear quarter under a sleeping berth. Remove the mattress, lift an wood panel cover and there it is. Both the original and replacement were glassed in but the flaps were easily cut or bent. It barely slipped in but I was able to do it and it fit perfectly into place.
I think I was really lucky to find someone relatively close in San Diego... I'm in Marina del Rey... who had the same tank.