The stock 3.90 geared rear end is plenty strong behind a v8. I believe I would change transmissions before I would change the rear end. A 3.90 rear end with a .73 overdrive will give tou an effevtive rear end ratio of 2.85:1. At 55 mph rpm will drop from 2476 to 1808. If you are changing the stock rear end because you want positraction, then that is a different story. I would go with the 3.73 gears you have, and still try to find an Overdrive transmission that can take that type of HP... like an A833 4 speed, or a tremic 5 speed.
