Hey guys! So I'm connecting an Xbox to an arcade monitor in this old Pit Fighter cabinet. The previous owner replaced the chassis so I have no idea what kind of chassis this is (pics below). Anyway the game in the cab was pit fighter and when hooked up via jamma to that game board the monitor looked great. I had to do a little edge convergence but the monitor is bright and crisp so I thought things were smooth sailing. The obvious choice for connecting my Xbox to this monitor was the Ultimarc adapter.
So I bought it and was really happy with the shipping (2 days!) and build quality. Here it is connected to my monitor:

There seems to be an issue though: there are diagonal lines, running from the top left to bottom right, jumping all over the screen all the time. It's really bothersome.

Visible here on the 'R' in the background

Video of the lines. A little hard to see due to clashing refresh rates of course, but this gives you an idea of the movement and intensity of the lines:
Now here's my monitor chassis. The tube itself says 'Zenith' on it.


Power supply/transformer for monitor:

Andy over at Ultimarc said it might be a grounding issue, so I added another ground wire from the 'GND' terminal on the adapter to the monitor chassis, then tried it on the power supply. A small difference in brightness occurred but the lines remained. Any ideas guys? Thanks in advance! The adapter is a great product by I'm dangerously close to pulling this dang monitor out and sticking a new CRT TV in the cabinet. I did this on my last 3 builds and it worked great via XBox>component video but I was hoping to make use of this perfectly good monitor.
EDIT: I'd be glad to take any additional photos or provide pertinent tech info if you need it.