I just did the lt swap. You definatly need to raise the motor. Unbolt the motor/tranny mounts and with the car on jackstands use the jack with a nice peice of 2x6 wood and jack the engine up. I installed both headers from below the car, I would also highly recommend getting a mini starter before you begin the swap and install it at the same time, I didn't and now i wish i would have because there is about 1cm of clearance between the header and starter. Also you may want to get some o2 extensions, i was able to play with my wiring and make it work but it is tight. Make sure your o2 wires do NOT come anywhere near the headers. You will also need some new header gaskets. Also like"Vikingpower" said the factory bolts can be a pain in the a.s.s. so if money permits that stud kit would be a good idea.
If you need to or plan to replace the motor/tranny mounts this would be a good time to do so. If you have any questions during the install feel free to pm me or just post it up here. The whole deal should take one days hard work but the benefits are worth it. good luck.