The 9" is a great upgrade for these cars. Most of the aftermarket guys building these get the brackets as close as the factory did. Paying attention to instant center is the critical to getting extra performance out of the chassis, even for a daily driver.
On a side note, one of our shop cars ('78 Malibu) was built in early to mid 90's. Flat top 355, 350 turbo, hard hitting shift kit, rear lift bars, aftermarket posi and 3.73 on drag radials. Car has been unchanged since the build with exception of tires. Rearend holding up fine.
On another side note, I blew up 5 stock 7.5" in 1 week just to prove a point , lol.