[Paul Rose]

Don't have a 289 or a Top-loader, but if the RPMs & speeds that you listed are correct for your current setup, then:

With 3.73 gears:

3.73 / 4.10 = 0.91

3500 * .91 = 3184 @ 60
3700 * .91 = 3366 @ 65
4000 * .91 = 3639 @ 70

With 3.55 gears:

3.55 / 4.10 = 0.866

3500 * 0.866 = 3030 @ 60
3700 * 0.866 = 3204 @ 65
4000 * 0.866 = 3463 @ 70