It appears I have the performance set with the underdrive alternator pulley / crank. 6060592 has about a solid inch too much slack. Enough slack whereas the a/c will not function and I get some totally awesome belt slip.

I ordered a 6060580. Anybody else have that problem with the "suggested" belt size?

 

My notes say I used a Dayco 590K6, but i'll be darn if I recall the belt length.

 

ya this was a goodyear. it should be in tomorrow, we'll see

 

just installed the 4060585 belt with the march 2pc underdrive crank underdrive alt set. MUCH better. no belt slip. This is the belt of choice for this job. hope this helps somebody