9 InchesThe 9-inch Ford rear axle has always been a desirable piece for enthusiasts seeking a reliable performance rearend. This big guy is a bolt-in swap for a lot of applications. Your greatest concern needs to be flange-to-flange dimension, which will determine fit. Spring-pad-to-spring-pad dimension is also critical. Get these dimensions from your 8-inch Ford, then get looking. Also keep lug bolt circle in mind while you are searching. Lincolns, to name one big Ford, have a larger 5-inch bolt circle, which won't fit your Ford's wheels in many applications.
Boss Rods?If you have your heart set on a set of Boss 302 connecting rods because they are stronger, consider the facts. The Boss 302 connecting rod is the same C3OE forging installed in the 221ci, 260ci, and 289ci engines between '62 and '67. What makes the Boss 302 rod different is rod-bolt size. If you simply must have Boss 302 rods, have your machine shop shot-peen a set of 289 rods and fit them with 3/8-inch ARP bolts. You'll then have the equivalent of the Boss 302 connecting rod in your 289.