search e-bay item # 400301081513 is that the ticket

I know this is old, but just saw your question now.

It has to do with piston speed mainly.

For example, a 496 "stroker" , will have a piston speed of 2125 FT per min at 3,000 rpm. A 502, will have a piston speed of 2000 ft per minute at 3,000rpm. At 6000rpm, a 496 will have 4250 ft per min, and 502 will have 4000 ft per minute.

It is piston speed, that sets the boundries so to speak. Thats why if say, you want a 5500rpm 502, you wouldn't put a 260/270 duration cam in it. There just won't be enough piston speed to match the cam events. Turn it to say, 7000rpm, and now you might have a better match.

Or , you can look at it this way. A 496 "stroker" , having a piston speed of 4250 at 6000rpm, to get the 502's piston speed to match that, you would need to turn the 502 to around 6400 rpm. So, if you were choosing a cam for a 6000rpm 502, and one for a 6400rpm 502, they would be different, the 6400rpm version needing more duration. So kind of the same concept on why a longer stroke, needs more duration to meet the same rpm level, even though the cubic inch is the same.

Thanks MT.......Im gonna go pour a drink..