Airbrush or Preval for touching this up?

When I had the header out I touched up the rust on the inner fender and discovered the spraycan mix was much grayer than the engine compartment.
I still have the cans of acrylic laquer used in the engine bay from years ago - and other than settling, the paint seems good.
Since I've got the bulkhead connector out, and can easily move the wire etc, it seemed like a good time to touch up on the firewall around the master cylinder.

I was going to get a Preval cartridge but then thought maybe an airbrush makes more sense.
Yes? No? I don't mind buying something if its better and I'll sue it again. I have compressed air now.

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