Another cam degree question

I have something similar, I bought it from Goodson. But there are plenty of ways to skin a cat. I have an indicator with about a 6in plunger, or I have a 1in travel indicator with replaceable tips, so you can customize your setup to your particular situation. Of course, it helps to have several types of magnetic bases and "linkages" to orient the indicators to fit around obstacles.
Coming off of the rocker arm would be less than ideal, but sometimes you have to make do with what you have.
I can't stress enough, you need to find the exact TDC to orient the degree wheel, and you should check the mark on the dampener, and match mark the inner hub and outer ring, so that if it should slip in the future, you will be able to recognize it easily.