Do you know if the 3.55 gear will fit into a triple locked 80? I talked to a shop and they said the locked 80 has different diff than the open diff, and the 3.55 will not be able to fit in there, unless swapping in the whole open diff rear axle.Good luck on your build. I’m happy to help in any way.
I do want to make a suggestion…..
I recommend you first install the 3:55 gears and drive/test it. If you still want the 10% overdrive, do that second.
I first did the 10% install thinking it would get me in the right range. After doing it, I wasn’t happy and then went to the axles.