[fiveohpatrol]

Your friend is referring to 5.0HO's to having roller cam's. The only mustangs to come stock with roller rockers are the 5.0 cobra's.
The roller cam uses roller lifters that basically have a wheel on the bottom of them that "rolls" over the cam. The non HO motor has a normal flat tappet cam

Roller rockers have a cylindrical bearing that the rocker pivots on and thus causes much less friction than a non-roller rocker.

The ratio (1.6:1, 1.72:1, and so on) has to do with how much the rocker will push the valve open compared to how much the pushrod is lifting the other end of the rocker.
With a 1.6:1 rocker arm, if you had a cam that pushed a pushrod up 1 inch, the rocker would then push the valve down 1.6".
I'm just using these numbers to clarify things, not that you would ever find a 1.6" lift cam.

Anyway, if you plan on installing a cam in the future, then I would reccomend the 1.6 roller rocker arms. This will give you a better choice of cams to choose from without having to figure out the lift that you'd get with 1.7 rockers. (the lift on cam specs are with 1.6rockers).