http://www.jagsthatrun.com/Pages/Parts_DAT200.html
The trans crossmember wont work if you are using a T56, if the donor car is an auto, it will work. You didnt specify which.
Depending on how their mounts are, you may have some interference issues with the a/c compressor mounting location.
Their speedometer cable you wont be able to use so dont buy that from them either.
Getting it running will be fairly easy, though the harness layout may not be ideal for the car, thats going to come down to the installer, etc.
Keep in mind the LT1's heads have D port exhaust, so make sure you get headers capable of covering them. Most 1.75" headers with a square port will do this, 1 5/8's you'd want them to be designed for D ports.