Did the seller include the stock parts, especially the advancer? It has the Top dead center mark. You are supposed to rotate the motor to the T mark, then remove the advancer and install the Power Arc parts and rotate the wheel until the led lights up. If you don't have the stock advancer, then you will have to resort to other means to find TDC. The seller of the PA once recommended using a soda straw through the spark plug hole when a member here got stranded on the road. There is No way to check the PA timing dynamically with a timing light.
Now, be warned, the Power Arc system is discontinued due to it's lack of reliability, and there is no support for them. I wouldn't trust one any further than I would be willing to push my bike unless I had towing insurance, especially if it's hot; the member I mentioned had two of them fail, and both times it was in the Arizona heat.