OK, Here is what I found on the 235 block that I am getting ready to replace my 1951 chevy 216 engine and trying to follow the original posted tech tip. Will this mental torture ever end? The 2 lower bolts removed from Inside the pan threaded into the timing gear cover were 5/16-24 grade 5 bolts. When I fit a 5/16 drill bit shaft into those 2 block holes, it is sloppy loose.That is the bore size I would use to thread the 2 holes to 3/8-16 as per tech tip. Going up in size in drill bit diameter, I find that a 21/64 inch drill bit just fits the existing hole. looking at my US Tap and Drill Bit Size Table, that is the exact size needed for a 3/8-24 inch bolt. Please, I already drilled out the Timing gear cover to 3/8 inch. Is my block a misfit? Thanks to all for guidance! Jerry
