Modern paint for a '48 Pontiac

[Humph7ey]

I resprayed both my Pontiacs about 18 years ago with cellulose and they have not weathered well in the French summers. I like them to look shiny as they are huge cars and take all day to polish properly. I know the colour formula, but it is in ounces.
Is 2K recommended for respray?

[Humph7ey]

Can I topcoat onto the cellulose?

[Humph7ey]

anything else I can use?

[Humph7ey]

Metallic same as original.
I do not think that stripping the old cellulose is an option as it was a bare metal restoration in 1999.

[Humph7ey]

Is 2K the only option?

[Humph7ey]

Thanks.
Any idea how much paint? It is about the size of a Rolls.