I have known people to do it ( I knew people who did it in high school, 318 with 360 heads but we didn't know anything either, I would venture to say it would run just as well with stock 318 heads.) and like I had mentioned if you have high comp pistons instead of flattop factory cast ones it works theoretically. One would never know unless you did dyno tests etc. In mine I listened to the old coot and ran stock heads, the only thing not stock on my 318 was the cam, the 600 Holley and the 2.5 inch exhaust with headers. it didn't run bad either. it ran better than most would think. I didn't race it though ran it on the street. the closest to a race was when I blew past my buddies 95 Chevy truck on a rolling start highway race. he thought he had something special, I dusted him going about 100 MPH. The dart was haulin azz that night. I remember walking up to a woman at a bar and saying "wanna go for a ride in a fast car?" that was my pickup line ahh the good ol days...:)