I have shot clear over a few older paint jobs before to preserve the patina look. If it's original paint that hasn't peeled or flaked and is just chalky then you can scuff it with red scuff pads and dawn dish detergent to get rid of the layer of "dead" paint and oxidation. This is critical to getting the clear to stick and last.
You can buff a spot and have a paint shop scan the color to get a close match, and if they're really good they can tint the paint by eye to get an exact match. You can use that to blend in any repaired areas before you shoot clear. I believe that's a metallic paint, so you'll want to use a blending solvent to keep the edges of the blended areas wet so the metallic particles in the new basecoat will lay down properly. Dry edges around the blended area will stick out like a sore thumb since the metallic particles won't be oriented properly.
I usually add a flattening agent to the clear so it's not 100% gloss. I don't like 100% shiny patina, but that's a personal preference. 7-8% flattener in SPI clear gives the look of well-buffed original paint. 15% gives a dull shine, and 25% gives a satin finish.
This is dad's truck that was scuffed and shot with 25% flattened SPI clear. I think 15-20% would've looked better.
My '63 VW shot with 7-8% flattened SPI clear.
'51 GMC with 7-8% flattener.
