[FullHawgPoncho]

Look for a posi or open diff with 3.xx gears. I have a 66 gp, from what I’ve read any full size rear end will work from 65-70, and 71-76 but the pinion is splined different on the later models and that would need swapped as well.

[PONTIAC LARRY]

Originally Posted by FullHawgPoncho

Look for a posi or open diff with 3.xx gears. I have a 66 gp, from what I’ve read any full size rear end will work from 65-70, and 71-76 but the pinion is splined different on the later models and that would need swapped as well.

to clarify i the housing interchange is 65-66 only as far as bolting up if referring to complete built axle , the gears and differentials interchange as you have it listed yes 65-70/71-76+yoke Pont B cars

[Steve Barcak]

Just a thought... You may not be aware but, low gear planetary gear sets are avail for thm 400s. there is a 2.75 low and a 3-1 low ad I think both use a 1.60 2nd gear and 3rd remains direct. Its a great way to increase acceleration of a heavy street car and have no negative effect on mileage, noise, engine wear, cooling, etc. I started using them in 1985 on one of my GTOs and loved it. Have built a few and now have one going into my 69 Bonneville Safari. In the long run, it is such a wiser choice over going with a deeper rear end gear. Hope this may help you and understand some other options.