Thanks, for the replies.
So far I am playing with 2 ideas for masking the flames off:
1.) Using very thin strips of masking tape to mask the outline and than cover the rest with masking tape.
2.) Putting a wide strip of masking tape/material on the body drawing on there the flames and than cutting the area to be painted out.
Need to collect more photos of actual paintjobs to see if I need to dulicate the breaker .line, as it would hardly be visible in 1/12 or 1/24 scale.
Don't think I will use stencils for the flames as I don'(t think that they will work for Bikes.