Just recently went through this with our '66 Lemans convertible with a Carter 625 cfm competition carb. Yes, it would be extra nice to have a period correct intake and carb. such as a Qjet or Holley, but don't forget that Carter was also listed as an option in the '66 chassis shop manual. Carter= Edelbrock in this day and age. Don't know what year Goat you got, but I ran that 625 on the old 326. Now it is on a '71 455. VERY small carb. for that engine; didn't ever think that would run the 455, but lo and behold... she run damn good now... Had a terrible time with it, checked everything under the sun: timing, dist., wiring, carb. rebuild-(three times) etc... turned out to be a cheesy Chinese crafted brass vacuum block at the back of carb.(attached to power brakes and modulator) that had a casting flaw and was sucking just enough air to make it run slightly higher rpms at idle and do all sorts of crazy things. One day it'd run great, next day terrible. Problem didn't show up with any amount of carb. cleaner spray. Had to disassemble that vacuum block and THOROUGHLY visually inspect it. Check basics first... VACUUM LEAKS, carb. gasket, ignition timing, fuel filter, vacuum port configuration, fuel pump pressure, float level, compression check, etc... You'll get to the bottom of it with a little persistence. You can rent a fuel pump pressure tester at most any auto parts store. Maybe someday I'll have a real intake and carb. on mine, but for now, this'll do.