Hey Brian- the paint nowdays are a lot different than the paint of old, they are more like film than paint. Follow the tech sheet to the letter and you will be ok, I like the PPG better because I get better coverage, as well as atomization. Omni is so thin you have to watch out for running, and sags. You should be able to cover your roadster with about two quarts of PPG's DBU/or DBC, and a quart of their clear, so your not talking about a lot of money difference.
If it were me I would go with the DBC BC/CC.......I wouldn't be happy with the finished Omni product quality just because it doesn't have any depth to it.
I've shot a LOT of both & I don't care for Omni- it's industrial grade- for industrial equipment. But -Good Luck, and I hope to see your hard work as it nears the end.........