4.10 gear ratio is probably the least common although they are out there. As far as the front and rear being the same for each vehicle, yes and no. Your BII will have a 7.5 rear axle. The Ranger 7.5 rear axle is not a direct bolt in, it is wider than the BII axle and the mounts will need to be moved. If you are mechanically inclined and have the tools you can to either, cut and weld new mounts for the Ranger axle or install the Ranger gear set into your current housing. You will have a Dana 28 front although I believe the Dana 35 may have been available in 89 and 90, don't quote me on that though. As long as you have the same third member as in your vehicle wheter it be a D28 or D35 all you will need to do is take your current third member out and install the one with the 4.10s, unless you just bought a ring and pinion then it will need to be installed inplace of the 3.73 gear set. As far as installing gear sets, if you don't know what you are doing nor have the tools it is best left to a person with the proper knowledge. If installed inproperly not only will they be noisy but will acceleate the wear of the gear set.
Matt
