I have a 68 firebird 400 that I have just rebuilt the engine in. The timing cover and pump was heavily corroded and was advised to change to the 11 bolt pump from the 8. I believe the upper brackets from late 69 to 70? Cars would fit because they were all 11 bolt??? As for the pulley I have look all over the web and the best match for diameter to the 9788886 pulley was the 9799128. After measuring both 8 and 11 bolt timing case widths and to pump flange depths I realised there was a differents of about 7/8inch (22mm). Depth of 9788886 is: 1.875” Depth of 9799128 is:2.750”( from web) Differents of 7/8 (22mm) The pulley is from a 1970 car used the same crank pulleys as on the 68 (Pulley # 9790842 and 970843). All the information I gleamed from chart from: http://grandprixchapterofamerica.com/tech/pontiac-timing-covers-pulleys-acc-brackets/ Please if anyone thinks I am going the wrong way with this please tell me, I am only going off what I can find on the web. One other point I may be wrong but wouldn’t you water pump and fan be turning slower with a 8” pulley than 6 1/2?
