This is a brand new tank, still in the box. The original looks to far gone and would need a patch (there's a hole rusted through). The new one looks to be raw galvanized metal with a light coat of oil (maybe?).
The old one looks to have been undercoated.
I've tried to think back to what the one on my original one looked like in 79, but I can't recall for certain. Not that it really matters. I'm not looking to make a show car out of this, but a nice weekend, fair weather, cruiser.