Check RockAuto.com for speedo cables. Here is a chart from the 72' Buick factory manual showing what was used with your 2:29 rear in a G-body. The 2 number columns at the right are DRIVE and DRIVEN gears respectivly. You will notice the RED gear (21 teeth) is not used, thus the adapter. It WAS used with the 2:14 rear gear with a 10 tooth drive gear. FWIW, one tooth on a driven gear is worth about 5 mph at the speedo. Another way around this is to compare the diameter of the factory tires versus the actual tires on your car now. You may find another driven gear is just what you need to get it all in sinc minus the adapter. http://www.wallaceracing.com/tire-aspect-calc.phpHere is a tire height calculator, and this site has the others needed to determine ratios and gears.
