Murf,
This is kind of a tough one to answer. It would mostly depend on the engine's Crank & Wtr Pmp pulley and, also the pulleys & mounts you are using for the Alternator & AC Comp. I measured around my pulleys with a piece of rope to get a rough estimate. Then I ordered several different lengths of belts and used the one that fit best. I have a 302 w/short wtr pmp, pulleys & Alt mount from CVF Racing and RCR supplied AC Comp & mount with 2 Belts, same configuration as you.
Rod