Michael,
I'm not sure ANSA or Arbarth ever made a system for the MGC. Do you have information to the contrary? I'd love to see it, just to compare what they had to what's out there now.
The Maniflow system, IMO, is the best one out there for the C. They have a dual system like fitted to the Downton cars, and I believe they have a single system also. They were founded by ex-Downton employees and have the same jigs used by Downton.
The downside of this system is the cost of getting it over here.
Perhaps Moss offers an equivalent. Their European branch offers a similar system to the Downton brand, or at least they did, so maybe they can get it for you.
My 2 cents.
Mark