'99 LS400 engine compatable w/ '00 GS400???

got a 99 ls400 w/ a blown block due to some recent flooding in the area. the local salvage yard has a 00 gs400 engine. my question is....would the gs400 engine bolt right up and work in the ls400? both are 1uz-fe...however...both long blocks has 2 different part numbers. if it does bolt right up....then what are the differences in the 2?

Well, first off, if the GS engine has a flywheel on it, make sure it bolts to the torque converter. if it doesn't have a flywheel, make sure it bolts to the flywheel of the LS. Even though they are the same engine, they have minor differences. The LS2 in the GTO and the Corvette produce about a difference of 50Hp dispite being the same 6.0L engine. Also, i would think you would need to get your ECU tuned to operate on the different engine because i am almost certain they modify the code from the ECU every new year