Hello, it means that the car would be raced with factory parts such as bias ply tires, exhaust manifolds, just to name a few. It basically has to run with the parts used when it left the factory. However, internally anything can be done. For example, I have a 440 sixpack motor in my 69 superbee that is a higher than stock compression and it's been stroked to 493 cu in. and the heads have been worked over but you couldn't tell by looking at it because externally it looks factory stock.

Thanks, Juan.