Ok, let's look at what we know about the 67 L78 alt. pulleys.
1- The pulleys where installed on the engine dress line so they would need a broardcast code for the line workers to install the correct pulley.
Examples: A- Z28 # 3829387 AI
B- L78 # 3844100 AK
The 69 P&A Shows both these numbers to be correct service replacement #'s and for application, but probably without the #'s or broardcast code.
So, all NOS replacements should be incorrect if they do not
have the #'s or broardcast code.
2- The 67 AIM A4 with a drawing date of 12/22/66 and a release date of 2/17/? shows that pulley # 3844100, fan # 3843346.and belt # 3849739 should be installed. The release date falls in-line with the 1st production of the L78 engine and there are no revisions recorded, but there could have been revisions around 05 that we do not have in the AIM. The 69 P&A backs all three numbers ( 3844100,3843346 & 3849739) as being good service replacements for the 67 L78 application.
3- The 69 P&A shows the Z28 (all sb) bellt # 3885047. 3/8 wide & 53 1/4 long and the L78 # 3849739, 3/8 wide & 55 1/2 long so the L78 belt is 3" longer.
This brings up the question. will the in question pulley 3829387 AI even work with the correct belt #3849739? Some say it will not,I need to look into this.
4- The 69 P&A shows that the # 3843346 fan was used on all 67,68 applications. Single reinforcement rib, black with 11 blades and 5 11/16 dia.