I like the M20 ratio better than the M21/M22 ratio so I'm going to order M22W. The M22W has the 2.56:1 1st gear.
See
http://www.autogear.net/m22ratios.htm
Year 1966-1974 M20 Ratio: 2.52 / 1.88 / 1.46 / 1.00
Year 1963-1974 M21 Ratio: 2.20 / 1.64 / 1.28 / 1.00
Year 1967-1974 M22 Ratio: 2.20 / 1.64 / 1.28 / 1.00