I don't know the gallons the tank carried, but there was a couple of VRCC'ers in California, someone added a 8" center strip in a split in the middle Valk Tank.
It was a wide mother. One of the tanks was on a Red/White, but I forgot his name. Went on a couple of Poker Runs with him and his wife. I'd stop for gas, and putin 4.3. They would get a water. Take off, I'd stop and get 4.3 more gallon and same thing, get a water. Get back to the check in and they would pull across the street and fill up for the trip home........
With gas weighting in at 8# per gallon, that has to be some top end weight to slosh around up there. Don't know if the tank had and splash deflectors inside of it or not, but it had to of been at least 10 gallon.
1st time I rode to Alaska, in 72, I'd of loved a tank that size on the old Cog-A-sock-i, ring-a-ding. Back then the road was so rough, it broke my fairing off the front. Got up to my son's in Anchorage, pulled out his welder, and added some stronger bracing. Must have been good enough welding job, as the bike made 2 more round trips. I gave it to my son when he graduated from the University of Alaska in 1977. I rode it up for the graduating ceremonies, gave him the bike, and he rode it down and back the next July or August for a visit. Then unbeknown to mom and dad he and Kathy got married. Married by a Justice of the Peace. They rode it down, she flew home, and he rode the bike back. She said her butt couldn't take that much of a beating. LOL

Kathy was an Army brat, she was born in Anchorage, dad left for another duty station and returned to Anchorage when she was about 20 or so, she never lived in one place more than 3 years. Her dad was a Colonel in the Army.