I am not sure about that one, but as far as I have gathered, you ONLY swap PCMs and either edit your harness or buy one of theirs(not much wiring apparently, simple pin swaps), so I have yet to read about needing a new dash.

The site says it'll work with a 4l60e, 4l80e and a t56. It also says with the proper pcm the dash will work fine.

I am seriously considering doing this on my TPI motor, although EFI Connection doesnt have any wiring options for the 3rd gen I would have to make my own harness. I started pricing out the connectors to make a new harness and you are looking at about $200 in connectors without any wire. I would really like to go this route because I would get the benefits of the LS1 without having to get new headers and exhaust to get everything to work. Plus on the Gen 1 conversion the sensors drive the dash rather than the ECM, with the exception of the speedometer. I would be looking at more like $800+ to do this swap compared to the LT because I would need the distributor.
I have been following the thread about this over on TGO for some time