Simple question. Does a Monte Carlo Bar bolt right in or do you have to dill any holes?  

It will bolt right in but you have to drill an extra hole.  Here is a pic of mine.  
 

99.9% of the people will not mind that hole. If you'r worried about "ruining" the car all you would have to do it weld fill it, grind, sand and paint. Nobody would ever know you drilled a hole there.  

That's true, and if I was looking for a classic Mustang and it already had the MC bar on it I would consider that a plus.  A 65 classic with a monte carlo bar and an export brace and a 4 row radiator with an overflow tank and a pertronix ignition system would be my cup of tea.  Oh Yeah, that's what I already have.  Is it a restomod?  Nah.  The body has not been altered, nor has the engine, transmission and rear.  She's still a classic. Any and all of those additions can be removed if purity is what you are looking for, but I guarantee you that you won't drive it 20 miles without heating up, or running off the road because you took a curve at the speed posted.