Depends on the race.
A '68 W-code fastback will eat a new mustang alive in 1/4 mile and top speed, with no glimmer of hope. On a track or road race the new mustang will win unless major work has been done to the 68's suspension.
Mine had major work done to the front and rear suspension, brakes, steering with modern rims and tires. It still couldn't quite hang because of the weight distribution. The big engine makes it nose heavy and impacts cornering terribly. I moved as much equipment as I could from the hood to the trunk and replaced all the front sheet metal with fiberglass. Even with all that, I never got the weight better than 70/30.
The result was a car that would pull .92G in a turn (not all that impressive), do 0-60 in 4.2 seconds, run 10's in the 1/4 mile and could top out at just over 200MPH (I have a pink slip to prove this). It would also drain a 20 gallon tank in just under 15 minutes running flat out.
Despite the issues, I miss that car. It was stolen and crashed during the joy ride with no survivors. One of these days when I am rich and famous I'll rebuild it, positioning the engine a little farther back this time.
