I tried wiring it up and the wiring and mod shown in the pic works.

Funny that this is the only bit of information I could find on using the amp with a Duckscan. The pic only and no other information.
Most of the info I found including Clay's repair bible only references the Wells Gardiner setups and shows the Duckscan cable pinouts and nothing more.
The pic came from a fellow with the user name of SOL50 on a pic hosting site and found it via google several pages in on a 'RFM CGA Monitor Amplifier' search. No explanation, just the pic.

I wired it up this way using Molex mini-fit connectors (Pin2000 spec) for plug and play so I can easily unplug and reverse the mod and had a stable picture but a bit of image warp distortion, certainly does increase the brightness and maybe a little bit too much I think.
I need to put a cap component kit through the Duckscan so I'll connect the amp up again after this.
Might see of Jomac has a take on whats happening here. I didn't take a pic but I will for Jomac and post it shortly.
 
So there you have it. Hope it aids in aiding somebody else's duckscan monitor amplifier add-on needs in future.
 
regards,
Cliff