Since I've done some 1:64 customs last months I think I have some pics that might help you...You will not need an airbrush for flames...Take a look at the pics below.The car close to a bit and the flames look great freehand with a brush!
What you think?
and here is another pic with simpler flames on a bike(the flames also close to bit scale)
P.S:And I think Shypo was talking about chameleon paint!