We had to increase the selling price on these center throttlebodies by $30.00 as we found when we ran these on the test motor that the transition slots needed to be machined longer. We had issues with these and until now didn't realize the problem. No hesitation coming off idle, smooth transition. Bases are fitted with new shafts, throttle blades and has the large center carb throttle arm attached. It is very unlikely our competitors are having these small center bases machined. If you have a vacuum leak around the throttle shaft you may only need to replace the throttleshaft because it is worn and not the entire throttlebody. Also have the front and rear 59-66 end carb throttlebodies on the web page and the large 66 center throttlebody. Comes with the neccessary gaskets.