Well, the JP's finally in caring Hands!

Removing that hideous finish is going to take some careful thought, and experiment, however.
If the tank butcher used acrylics, then you could probably use acrylic thinners to remove the surface gradually. Whatever you do, try your chosen cleaner out on a small patch of the tank- before launching into a major paint purge. I don't use enamel paints, but again if
they were used, the appropriate thinners, used judiciously, should get the results you need.
The very last thing you want to do is
dissolve your new foundling. Experiment on some detachable (and replaceable) part- like a wheel, for instance.
"Get your facts first, and then you can distort them as much as you please"- Mark Twain.