I've got a friend that blew his motor around Thanksgiving in his 96 GT. He brought it to them to have a 98 block rebuilt with P&P heads and forged internals. It was supposed to be done by Febuary, then March. They told him that it was ready to put in the car at the begining of April, but two weeks later they said that it hadn't even gotten out of the machine shop! He said he will never let them do any work on his car again. He's going to have it tuned at True Blue when ever it gets done.
Our other friend made a deal with him to get his C&L and all Excessive had to do was to ship it to Blacksburg. Well after two months and countless phone calls he finally got it.
I personally have no experience with Excessive, but I'm just relaying stories of my friends. Up until this thing with the motor, he didn't have any problems with Excessive and recommended them, but now he tells everyone to steer clear.
If you're going to just have gears installed, I would believe that it should be fine because they do have a decent rep. I'm not sure about leaving a car there for a long time though.
1996 Black Cobra Vert: sitting in the garage for now
2008 Black Nissan Altima 2.5 S: new daily driver