Kay'
here's the thing on primer, as the others mentioned it is pourous & will absorb moisture, and likely will fade to some gray or brownish color fairly quickly as it won't be able to take the uv's.....alllllso.....because it is primer it is most likely engineered to be easy sanding and therefore won't likely be very resistant to any type of abraision.
Automotive paint's with flattening agents are a kinda hit & miss thing. Oft times it'll end up dryin' blotchy some spots semi gloss some flat, unless ya got a way to keep the paint constantly mixing both on the bench & in the gun whilst applying it.
I would look at going the way of one of the engineered products such as the "flatz"
products previously mentioned, I also seem to recall a product advertised somewhere called "hot rod black" i think it was by evercoat. However if you are in kind of an experimental mode why couldn't you use say like....tremclad or rust-oleum in a flat black
& spray it on, it's like what 35-40 bucks a gallon. just real slow dryin' is all.

BTW.....whatcha gonna do for wheels on the truck, moon's & trim rings always look good with flat black particularly with wide whites...but the red wheels are kinda gettin tired, were it me i'd go with either apple green or aqua.
Mikie
near ottawa canada
58 merc 100 panel & 64 econo p/u