JR Sealey's 1988 Visa Pontiac 1:64

Fender Decals- Early on they were not used at all and even when they did, there were very few.
Positions- If your numbers are too far forward or there is not enough space to apply your decals without making it look like a car from IMSA, that's OK. There were many cars from that time period that had decals crammed all the way to the front fenders.
Paint Schemes- Less is more. Just hit the high points and let it go.
And Lastly, Do Your Research!!!- Study the cars from whatever time period you are doing and take note of their imperfections. It will allow for a more period-accurate car.
