But if your block came with 516's, adding these heads will really drop your compression. Since the 516 had smaller chambers
Also hardened seats are not a requirement, unless you tow or have a motorhome. Larger duration cams in a car, also with correct tuning run the exhuast valves cooler. Along with less driving we do with these cars, you'll never need them.
Stock 2 barrel 383 had 8 to 8.5 comp at best.
