So from what I've gathered Alkyd and Synthetic enamel are the same thing. The lead in this paint provided UV protection, so that is gone. Supposed to fade in sunlight.
Tough paint....painted my frame 12 years ago with primer, added top coat black....stored outside 4 years...looks amazing....
Ran across some Duplicolor quart paints at Auto Zone, I'll be using it to paint the inside floor pan on my Ford soon. Supposed to be a lacquer base.
Rustoleum is great for frames and a lot of other things. I shoot it, cut with acetone, with valspar enamel hardener. I won't use it as a topcoat for cars, floor pans are fine. there's so many available inexpensive enamels and urethanes. Cut the last coat with some matching clear and it lays out nice and holds up well. After the time and energy to prep the car, I'll spend more for paint. If you insist on using "tractor enamel" valspar is a little better than rustoleum. Keep us updated.