A body sports car handling

The reason you can't buy a Mopar "MonteCarlo" bar is that Mopars are much stronger in the front end than Mustangs (almost nothing from Detroit in the 60s was flimsier than a first-gen Mustang). Now, when every little detail counts, sure it's not a bad idea, but it's not necessary in most cases like it is on a handling Mustang.