Jim,
The 248/248 duration is as you guessed. The only problem is that there is no way of knowing EXACTLY what the duration is unless they make it relative to a certain amount of tappet lift. For example, your cam may have an advertised duration of 248 degrees, but at .050" of tappet lift, it may only be 215 degrees. Most cam grinders will offer the specification at .050" lift, but if they don't mention it, than you have no way of comparing one cam against another. Sort of like apples and oranges. More duration increases torque in the upper RPM ranges at the expense of lower RPM operation. Affects idle quality too.
The lift of .521 is once again apples and oranges. But I would assume that this figure is measured at the valve stem with 1.6 ratio rocker arms. But then again, if it ain't specified, how do you know?
The 602/602...... no clue here
The 108 degree lobe centers is the amount of crank shaft degrees between the centers of the intake and exhaust lobes. It is also related to valve overlap, or the time that both valves are off their seats. (The intake valve opens before the exhaust valve is completely closed)
A cam with lobe centers of 112 degrees is in the catagory of a good street cam; good idle and good vacuum at idle. One with 108 degrees will be in the catagory of a performance cam; lopy idle, with an increase of peak torque and horsepower.
Hope I got that straight...
- Jim -