The TREMEC book has an easy formula for calculating cruise RPM and shift points: RPM = (mph x Differential Gear Ratio x 336 x OD Ratio)/Tire Diameter in Inches

The "336" is just a unit factor. For example, my '33 at (70mph x 4.11 x 336 x 0.64)/31 yields 1996 RPM. For shift points put in your individual tranny gear ratios in place of the OD ratio, like my shift points at 3000RPM are 23, 36, 53, 67 and it'll hit 105 in 5th. I built a little Excel spreadsheet when I was chasing my ratios - I can e-mail it to anyone that wants it, or there are lots of calculators on the web (forum does not allow Excel file attachments).