I have an SLP tool, and I never use it. I use a straight edge long enough to go across the back of both clutches. Put the straight edge on the primary, measure the distance to the back of the secondary. Push the secondary toward the sled when measuring. It should be 5/8" (1" with electric start). You can measure both the front and rear of the secondary to determine if the clutches are parallel with each other as well. It worked as good as the tool does for me.
I found many years ago as soon as you sell off a tool, you will have a specific requirement in the next week for that exact tool. SLP sells 'em for 30 bucks, not bad. This one is a different style than the one I have, and it's supposed to be more accurate, which is probably why I had as good success just using a straight edge across the back.