Older mopar performance magnum 360 crate motor. Need to freshen up the hemi orange paint. Which is my best option?

Likely they sprayed those with the cans of MP engine paint. I think they still sell those, but beware that the colors are not consistent from can to can.

You could always have a paint store mix up a small amount of autobody grade paint and then spray it on with a Preval sprayer.

the last pint of hemi orange I had mixed up by a paint shop was about $235.00, plus reducer and activator...Tim

I just bought a pint of 69 440 hemi orange paint from Frank Baldason. It was $70 plus shipping. His mixing instructions were very different from my normal. They said use very little reducer and no hardener. This is to match the low gloss factory look. He uses PPG shop line. My customer wanted better durability and a little more shine so I thinned it more and used hardener . It was 95 degrees when I painted. it I could not get shop line so I used the Omni line. It came out quite well and cost about $100 total. Much better than a spray bomb.

If you'd like the exact paint code that was originally used, I can tell you PPG 3116 single stage enamel was used on the older Cummins built crate engines.

It comes up in the computer as AMC Mandarin Orange. I asked but couldn't get them to do that exact shade in lower cost (like Delfleet) enamel anymore.
If you want it in single stage urethane, PPG can do it in Shopline at a reasonable cost.

I shot this one with PPG Shopline single stage, with Matrix black epoxy primer underneath.
If it looks thin, that's how I shoot them purposely.......I can't stand the super thick "dipped in plastic" look on anything I personally do.

It's ironic the MP spray can paint was considered to be not quite good enough for the crate engines back then, by MP itself.......and they were shot with PPG from a gun instead.

I shot this about 10 years ago with paint from Frank Badelson. It is still holding up very well.

They probably mixed about 2-5 gallons in a paint pot, goes about 15 times faster and easier than a rattle can, its about production and costs, not what they have on their performance catalog.

Another vote for Frank Badelson. I uses a little hardener to help with durability. I shot a couple of test panels and didn't see much difference in gloss when not adding hardener.