I am not sure but could you possibly post a picture of the carb? Is it a vacuum secondary or double pumper? My 69 Cobra has an 850 on it and Jegs has the number that is on that Carb. I used to have a list of Holly numbers for their carbs in the 60s, but if yours was custom made even if I could find it I am not sure it would help. If your issues aren't the base being warped or something worn out, you could have a good racing shop rebuild it. The Carb Shop in L.A. has built some for the racers around here and two for me. They take the Holly's and rework them which is what it sounds as if yours may have been if it was on a NASCAR engine.
Ron
