He is pretty much going to have to change it all over anyway. Keep in mind the floor pans are a different shape in the 98+ cars, may make exhaust routing an issue too. Although it may just be the bracing, the pan might be the same, but check it out. You will also have to swap over your suspension too because the LT1 is alot heavier then the LS1 and will probably cause the nose to drop. At the very leastyou will need a spring change so a V6 car won't make much difference.
I've got a better idea, sell your stuff and get an stock 01-02 LS1, pick up a few tenths at the track to boot
