On the first version of a machine I used a timing device that cost $150. It works great but...$150!!! The 160 RPM shaft is 1" dia. and there are two pillow blocks with the sprocket outboard.
On the second machine, I cut the shaft in half and drilled the cut ends for a 5/8-11 thread. It was done in soft jaws so the holes are very concentric and the shaft runs true. I milled six flats on the ends of each half-shaft. A threaded rod and two lock nuts hold the shaft together. To adjust the timing, I loosen one nut and advance or retard the shaft then tighten the lock nut. I hope somebody else can use the idea. (Yes, I did shorten the shaft by two inches to make up for the nuts)