Here's how to retexture these bodies in Blender for anyone who's curious:
Technique 1:
Pick a body, then delete the other two. Then replace the corresponding body textures with your own custom texture. The bake textures correspond as follows.
Going left to right:
Chevy (First Body) - Front: TTChevyFront.png Body: TTBulkBody.png
Ford Slim (Middle Body) - Front: TTFordFront.png Body: TTSlimBody.png
Ford Balky (Third Body) - Front: TTFordFront.png Body: FordBulk.png
For example, On the Slim Ford, TTFordFront.png would be replaced with another front texture, and TTSlimBody.png would be replaced with another body texture.
Technique 2:
Select the body in edit mode, select a face on the part of the body that you want to replace, and hit SHIFT+G to select it, then replace it in the UV window. Do the same for the other half of the body.