If you can, test on a scrap piece or an inconspicuous area first.

It occurs to me just now that we (the responders to your thread) are providing suggestions which have limited usefullness given that we are unable to closely examine your tank.
You have the option to bring it to your local professional automotive paint outlet for opinions.
I suggest that you call first to get a good time to come by, and then tell them you are coming.
Having worked with guys and gals in this field for decades, I would predict that the opportunity to examine a  vintage piece and offer opinions would really energize their boring rountine. 
Ask "everyone in the room" for their opinions.

In my town of Syracuse NY the NAPA Paint Store (a professional outlet) carries the SprayMax products right on the shelf.  They have always spent time to answer any questions I have for them.  

Decided to wipe lightly with acetone and to go for it. This is by far the best spray paint I ever used, no runs first time ever, 

 

Nice work. 

Came out great, sorry I'm late on the response but I did an rubbing alcohol wipe down + 2k clear on my tank to preserve what was left of the paint/patina and it's still going strong three years later so I think yours will hold up well!

Looks great !  
Congrats.

Acetone would certainly be effective, but it is a powerful solvent., so I would not use it on your next job. As was suggested, alcohol or a pro panel prep. 

Next time alcohol for sure
acrtone is a bit too much 
happy Easter 

Looks like it came out nice...  that's what matters the most! 

I just bought what might be the last "250" decal on earth for the oil tank!