Well this might get you going for now.Till you find the right one. I use the 6'' Spectre base and filter. I can't remember if the stock is a 9 or 10''. The carb opening is 5 1/8'' the early AFB's were 4 7/8'' for the metal base.I had plans to use a Slant six base and graft the Spectre base to it. The slant and the 273 4 bbl uses the same filter.