How much is too much? I refused to buy a completely NOS Candy Gold CB350 tank for 375 bucks + 75 bucks shipping. I can have mine sealed and painted for about 200 bucks.
And this is because the tank is in bad shape. My CB750 have some small scratches but I will leave it like that. If you have a new tank then use it. It will profit you more being shown than being kept in a box.
I can look for the latch number but don't waste your time asking for it, it was superseded long time ago. You will find it on eBay listings every now and then. Surprisingly, I'm tracking a gas cap and latch that ends in one hour and is on 24 bucks now. You can always buy a rusted tank for five bucks, and tell the seller to remove the latch for you, send it, and discard or relist the tank if he wants...
Those latchs are made of "plastic metal" -whatever the real name is- and my impression is that, sooner or later, they break. I recently posted that I removed the one of my CB350 tank before sending it to the painter. I was lucky to remove the rivet without drilling but, unfortunately, I slightly bent the latch because of the punching. A slight pressure with the pliers trying to recover the original shape was enough to break it. The lesson? Buy a 30 bucks lock latch that will outlast me, and find a cheap thumb latch for in case my gransonds want to restore grandpa's bike to original condition. Live and learn...
Raul