I did the swap about 2 years ago with an 8.5 corporate rear end. I ended up determining it was from a 73 Nova, but why were the perches wider? Seals fit the application for a 73 Nova, but I am not 100% positive.
The rear end width was exactly within 1/4" of my 8.2 original. I just had a welder move the perches in about 1 inch. My gears are 3.42
I had a brand new driveshaft built as my old one was too long. I opted for a new one because it was cheaper to build a new one that to try to shorten and rebalance the old one.
When the welder moved the perches, he actually bolted the rear end to a table and made a jig that put the new ones exactly where they needed to be.
When I put the new rear in the car, it bolted up perfectly.
Even with the stock 400 the car really rips compared to the old 2.73 open rear. Also I run with an M22 4 speed.
