Backdating pulleys
 

Is the fan belt shoulder shape different between the '74 and the '79 half pulley? These pulleys appear to be the same, but the '74 half pulley is $20 and the '79 half pulley is $60. The original double fan pulley is slightly bent from tool torque, and I want the cleaner appearance of the single pulley. No smog pump.

Also, can I remove the lower A/C pulley and use a shorter bolt on the crank? The A/C pulley is very heavy, and I wonder if it serves some purpose other than to drive the compressor?

The fan half pulley has a different ratio and the later half brings the belt closer to the center. The count of holes in the fan halves is the give away.
The ratio was changed in 77 with the 5 blade fan and the larger crank pulley and the 725mm fan belt. The 78/79 fan uses the larger crank pulley but a smaller fan with 725 belt.
The 80 and later went back to a larger fan and the smaller crank pulley along with going back to the 710mm fan belt.
Removing the A/C drive on the crank pulley, its heavy but usually cast with the fan as a unit.
There is pulleys available without the air drive.
Bruce

So the '74 half pulley has the wrong shape for my SC fan, I guess it's an SC fan: 16 holes, the only stamping inside is 18 over 78. I need the half pulley for the '78-'79. Correct?

Regarding the crank air pulley, it is a separate piece and very heavy. So it's okay to simply not install this pulley and get a shorter bolt?

Take a look at this pulley:

DZ 935 Crankshaft Pulley - Fünf Gruppen Forums

Or a half pulley 80 to 89 removes the airpump drive belt and cleans up the fan face.
Bruce

Thanks! Fan half pulley should be here Wed.! Got a shorter bolt for the crank pulley so I can run without the heavy AC pulley.