Ok guys, I'm not an expert so don't shoot me, but this is what I have found out. Disk Brake master cylinders from 67 to 70 had the recessed hole for the long rod from the booster. 71 and on used the short rod. There is a big difference in master cylinder appearance from 67 to 70 depending on year and whether or not it was for disk or drum brakes.
Master cylinders for 67 to 68 disk brakes are tall and thin with an oval cover held on by two bails going from side to side.
Master cylinders for 69 to 70 disk brakes are short and wide with an oval cover held on by two bails going from side to side.
Master cylinders for 71 to 72 disk brakes use the short rod, and have a rectangular cover that is held on by one bail going from front to rear.
Master cylinders for 67 to 72 drum brake cars are tall and thin, have an oval cover that is held on by one bail going from front to rear. They also use the long rod.
One thing to note, just because you find a particuliar combination on a car does not mean that it is the way it came from the factory. A lot of things get changed over 30 years. A lot of boosters and master cylinders are taken from other GM cars such as Old Cutlas, etc. They do not necessarily have the same configurations as Chevelles. Assembly plants did not always use the correct parts depending on shortages, model year changeovers, etc.
Bob Murray 66 Malibu
Greenfield, Indiana (Indianapolis)
TC Gold #49
[This message has been edited by Bob M (edited 03-01-2001).]