Well, upon further investigation, I have to say this tank is worn out for sure.............
I cleaned parts of it real well, and.... the pits are at least halfway through the tank. The tank is 2mm thick and the deeper pits are 0.8mm deep, add to that, I'm sure there is some rust on the inside of the tank and....
Not worth the trouble...........
I did find this on auction here..........
$30 now, and that is dirt, grease, not rust on the tank.
I've asked how much they want to ship it to Tokyo, it is in Fukushima, not close, not far.
If I get this tank, I'll clean it up, and reassemble everything, then either put it in the bike garage for a spare, or sell it...
Wish me luck!