I agree 100 percent on you decision to not modify your road runner. Too heavy and of the caliber it should be preserved and enjoyed as it is. Plenty of fish in the sea to modify.
The 69 mustang you posted is neat.
If I was to do a early mustang it would have to be a 65-66 coupe as my parents bought a new 65 when I was 10 years old.
Getting old just means you were smarter than some and luckier than others.
