Timing mark
As said if there is a OE type pointer that will bolt to the dr side then that is perfect & find exact TDC on that side & make a white paint mark across the dampener just like the OE slit is on the other side & you're set. If you have a dialback that is all you need but I would suggest make several addit'l white paint marks for 10-15-17.5-20 and 36 even with a DB plus in my exp they can be off a degree or so. 0.0632683" around the circumference is (1) degree & you can cut a strip of thin white paper measured with your calipers to use as a ruler to make addit'l paint marks or the timing tape & as said clean the dampener surface well then install it then spray it with clear lacquer to seal it so it stays put.