I'd probably use PPG DCC single stage or Delstar acrylic enamel. I have a 400 sbc that I painted with DCC back in 2007. It's still very glossy looking. It has flaked a little on the smooth machined surfaces, like the deck surface where the heads don't cover everything. I can touch it up with a foam brush and it will last for a few months before it does it again. I put a thin coat of DP90 Epoxy primer on it first. Some say to use primer and some say not to. I did, but just went with one light dusting.

I used a Preval sprayer to apply the paint. Works well and easy to control. I think a Preval bottle filled close to the top would do a complete engine. I bought a quart and have lots left over. Buy a pint instead.