I'm looking to use an older Sanyo 20EZ monitor with a JAMMA board. I don't have that stock inverter board (or even a flyback cage for that matter). I was wondering what the best option would be to allow the CGA Signal to work on it? A stock Nintendo inverter board? the parts kit? any third party solution i've missed?
What is my best option and why? 
Best option would be the Nintendo inverter board. Contact Buffett on KLOV, he probably has a spare he would be willing to part with.
The flyback cage isn't required, just keep your fingers away from the flyback and high voltage section when the monitor is on

The pitch of the signal header on the Sanyo chassis is .1, so you'll need to make an adapter for your Jamma harness video connector. Take note of the transposed color signals on the Sanyo, the order is not R,G,B (can't quite remember what it is).