I have not heard of any 427 COPO cars with the CY trans. I wonder if the CY was only used with a 3 series rear gear and not the 4:10? There is a copy of a Chevy Bulletin dated 7-12-68 in the Colvin book page 291 on this new HD "high speed" THM400. It states that the trans will "accommodate engine speeds up to 7800 RPM" and Max upshift point is 6300 RPM.
What was the code on the 1968 COPO L78 Novas? Also there is a question in the TECH section on what is the stall speed of the hi po torque converter. Anyone know? I could not find it listed anywhere.