Yes, as far as that manifold, I have seen it. Unfortunately as a performance piece, it wasn't good. I know nothing of it as a MPG piece though.
I always am happy when I can get 20 mpg, so thats my target. I realize I won't get that around town, I'm realistic. Also, I don't have an OD . . so I think 20 will be a great accomplishment. I also believe for me to get that, I may have to switch gears. I do some traveling every month and would love to take the BII sometimes, so highway mileage is a goal.
I don't remember what my '82 RS got in MPGs, I'm sorry to say. It was good. However, I have a heavily modified '82 GT now. It runs 12.8s. When the engine had less that 100 miles on it, I took it to Indy for the SAAC convention. I got 24 mpgs running about 65-75 MPH. I was tickled that an engine that had that much performance could do that well. However, that is with a T5 and 3.55s.
I have an HO engine I'll be putting in a Fairmont soon. Just for grins and giggles I'm going to run a Quadrajunk on it to see what kind of MPGs I can get. I'm running the stock HO roller cam with 1.72s, some slightly ported E7s and headers, so mostly stock. I'm curious to see how the tiny primaries work for me around town and such. My heads on the BII engine are also ported E7s BTW.