I assume you resoldered the many numerous bad solder joints this chassis is well known for when you had it out to do the capkit? Especially bad joints are at the connector male pins for both the video interface board and the "hor/ver" board. Same goes for the female connectors on both of those same boards too.
As to the momentary green flashing, it's a strong possibility the picture tube has an internal short which is momentary. Connecting the tube to a picture tube tester/restorer will confirm it and sometimes can cure it. It's also possible that a bad solder joint on the video interface board or bum transistor on it can cause the same problem, but I don't think this is happening in your case. In my experience I'd be 99% certain the flashing green is a internal picture tube problem.