You can use heatgun on low setting to take of the decals.
The biggest issue is to get rid of the glue residue, citrus cleaner may work.
To place the decals on the correct location, you can spray on some soapy water, slide the decals around where you want them, and then use a towel to softly touch the body and remove the remaining water.
For lexan bodies I do as follows:
Cut the body and make holes for body posts.
Sand the edges of the body.
Wash the body in hot soapy water with dishwasher sponge, I never use the coarse side.
Let the body fully dry.
Mask the body, windows, lights, etc
I always have the body at room temp.
In cold weather I heat the spray cans in bowl of hot water before use.
I always spray outside due the odour, but if it's below 15ish degrees, I take the body inside to make it dry between coats.
I spray only light coats.
Remove plastic cover when the paint is dry.
Add decals.
I hope it helped.
If the orginal decals are hard to find/expensive, there is several that makes repro decals including MCI Racing which is the most known.
