Save the Flows for the 5.0s. I had the American Thunders on my 87 LSC and it was stupid loud...and they flowed for crap. I then swapped them out for some Dynomax Ultra Flos and could actually feel the car pull harder in the upper RPMs.
You can get a deep sound with Magnaflows, too. It's all in how you set it up and the size of the mufflers, i.e. running a Magnaflow muffler in place of the resonators with no mufflers out back. NickT88LSCs car has just a longer "mid" muffler and it sounds pretty damn good. Not like a small 3.9 at all.
If you went with the size mid muffler I had on there before I took it out, with no mufflers out back, it would be pretty growly. Not sure on the size that was in there, think it was 14" long or so?
EDIT: found the info on the muffler I had in there - 11 inches long, 4 inches high and about 8.5 inches wide.