The Factory blueprint cam would be better with your 516 heads. I doubt that you have to
cut the tops of the valve guides or machine the spring seats. This cam takes a single spring with a damper insert. The 516 should be okay with this cam, depending on gearing, size of carburetor, intake manifold type/exhaust setup and intended use of motor. With the other two Lunati grinds suggested, (due to the HIGHER LIFTS ) you may have to do the machine work on those earlier 516 heads, since the pocket areas and exhaust valves are smaller (1.60 vs.1.74 later head). The remedy may be to pick up a set of later 906's or
452's (responds best to the bigger valves and template porting - thank you Steve D. and dogdays, I AM a student! ) and rework them to the way you want them! I do not have the link for the 383 article, but you can buy a back issue from Engine Masters. Great tech and cost/performance comparisions! A good ignition tune and timing setup, will NET great response and good power in you 383. Again, DO the research and USE the tech archives wisely. The trial and error tuning should be done in the car once the motor is up and running. Then you will see what the motor likes and dislikes under load and real-time driving. Suggestion: ALWAYS keep a baseline (starting or reference point) figure BEFORE you make changes, it would definitely make life (yours and the engines') much easier!