That tank is a hacked around early Manx tank. These tanks with the narrow V (albert modified) at the front of the tank was fitted to pre 56 Manx Nortons without oil in the left down for primary chain lubrication. The later frames needed a wider V to avoid the oil filling point.I have two good pics of the bike, one in 1965 when Bob Wier the original owner raced it and one from 1974 when Edward Bilton Smith owned it. Some time in the 11 years the oil in the fuel tank was added. After taking a good look trying to figure why the tank was so heavy at first I started to think it was a glass reproduction, Tapping it all over it sounded dull and thick but the sound lightened up as I went up the sides and parts of the top sounded metallic, also there were cracks along the perimeter of the tank on the bottom. On the longest crack 3" I used a small scraper to open it up and what looks to be bondo or some kind of filler started to separate, some of the filler is semi-soft and some is hard. Using a heat gun I start to remove it to see what's going on, the tank has been opened up so far in two places and then sealed with some kind of white sealer. So now I'm going to finish stripping the bottom then figure what the next move is. I'm seriously thinking about removing the oil filler cap, oil/fuel divider and oil vent and putting it back to the way it was (the divider is glassed in by pouring resin in the tank and rotating it). I did not want to go this far but the work done is horrible and the tank is really heavy View attachment 94065
Its probably worth reinstating the rear section as was, if you can find someone over there to do it correctly. Or send it this way and I can have it sorted for you. Or leave well alone and have a new tank made and put the original tank in the heritage box.