I am in the planning stages of replacing my 7.20 : 1 single speed rear axle gears with a 2 speed 6.40 :1/8.40 : 1. My truck is a '57 5700 with the GM 15000 lb. axle, another member has a doner truck, a '56 6400 with the GM 15000 lb. axle with the 2 speed pig. I have measured the bolt spacing on both pigs, they are the same distance from each other as far as I can tell with just a tape measure, it is difficult to see if the shape of the mounting flange is the same but they are close. My axle housing has square tube ends, the doner axle has round tube ends, spring center to center specs are the same, center of housing to center of U-joint are the same. Can I swap the pigs or are the housings not compatible, anyone here have experience with this procedure? Thanks for any advice.
