timing a 318 w/a 495 lift cam!!!!!

...I can see this is going to be a long day.... :)
What he meant "by shaved heads" is the milling down of the the head surface where the head mates to the block (the intake manifold surface should also be done as well to maintain proper engine geometry so the intake manifold bolt holes will line up. Ratios for the cuts are in the Performance manuals). This, in essence, increases your compression ratio by decreasing your head's quench area for each piston.
For what its worth, a 318 for street use really doesn't like a whole lot of cam without some serious mods and thats probably one of the biggest mistake alot of folks make in hot rodding them. With that big carb, high-lift cam, unmodified 360 heads and probably a stock street gear, you're not gonna have much grunt on the low end....a souped import would probably walk away from ya on a dead stop standing start.
It takes the whole combination of the car (right carb, motor setup, gear ratio, suspension etc. all working in harmony) to make it run like a scalded dog.....
A 650cfm carb, a less lift on the cam, a good street gear (I like 3:55s or even 3.91s) and a good set of milled 360 heads will make for a sweet street machine. How do I know??...lol, I've run various combinations of Chrysler's small block since 1968.