I installed mine in my garage with no real issues. DT's instructions tell you to unbolt the motor mounts to lift the engine slightly, I lifted one side 1" & then the other to get the headers in. That's two bolts per side, no big deal. Starting the nuts, there were two or three on the center tubes behind the shock tower that you had to do with the index fingers of both hands. Torque wrench, I was only able to get on about half of them, the rest I matched by feel with a flex head box ratcheting wrench. Std sockets are too short to clear the studs, deep sockets interfered with some of the tubes. Somebody mentioned the Sunex swivel impact socket fit really well. The air tubes are in the way, so 05 and newer like mine are a little trickier.
If they think they need to pull the engine, you are at the wrong shop.
I'll also say, the more I drive it the better I like the LT, Y pipe & Gibson setup. I wish I would have bought the side exit version but didn't know any better when I bought it.