I don't know what size the shaft on the Chevy is but on the GMC the manual talks about reaming the bushing to .3135 to .3160 inches in diameter. The shaft passes through the valve (flapper) and is welded to it, so the shaft may need to be larger than a 1/4 inch in order to fit properly. I had to free up the shaft on the replacement manifold I got and re-weld the valve to the shaft. It might be easier when its all said and done to get another manifold or the shaft from one. There are a lot of people who are up-grading to Fenton headers and probably have one sitting around.
