Disconnect the battery, raise the car, undo the motor mounts, raise the motor up, slide in the headers, get the end bolts on either side started, lower the motor, finish install.
Seriously, it's a 2.5 hour job if you've done it a couple times, or a full afternoon if you haven't.
BTW, most clearance issues with LT's are due to crappy sagging motor mounts... While you have them undone and the engine raised is a GREAT time to replace them.
The new design MAC's may not *require* the engine to be raised, but trust me, it's quicker and easier than screwing with the steering shaft and trying to get the car high enough. Plus you're going to be replacing the mounts anyway, right?....
You don't need a pro shop to do this, if you've got basic mechanical skils and a half decent set of wrenches and sockets, it's a do it your selfer.
Save the $300 and put it towards having a set of gears installed. THAT you might want a good shop to do.