I have a LS2 in my 65. As top fuel says, you won't regret it.
I have all the factory instruments working.
You need to use an older model temp sender (100 ohm in boiling water. The late model senders are 200 ohm in boiling water) You also need to keep the LS temp sender for the ECM to use.
I tapped the oil cooler blockoff for the the oil pressure gauge
I run the original truck wiring as a 60 amp circuit off the LS wiring so the amp meter works as is
You need to use a 30 ohm fuel level sender. I put 2 in my tank, the 30 ohm and a late model one for the ECM to use
Finally the converter for the speedometer is made by CableX and converts the VSS signal from the transmission to the correct 1000 turns per mile to drive the speedo cable
Details are in my build thread if you need them.
Good luck,
TR