Having no experience with monoline past or present, I do have a suspension that is one of the Stanzel Brothers systems. Starting with 'G' line I beleve they had at least four different variations. The Stanzel Flying Model Museum is still in operation, located in Schulenberg Texas as is their web site.
I would contact them directly with those photos and they may be able to shed some light. Do you also have the matching onboard device ?
John