That style is still available from Iskenderian (PN RATIOCOMP). In a more modern vein, Summit Racing has an online gear-ratio calculator ...

Mathematically Determine Your Gear Ratio For Any TrackPeople who have built and tuned race cars for years seem to develop a sixth sense when it comes to choosing rearend gears. Gearing is one ...

Would first gear go ... relate the chart to. It might help to make a similar chart for your current car just to compare, and to play around with putting different final drive ratios into this ...