Neither. Sell the car and buy a later LS1 car. It will be much cheaper & easier in the long run.
But if I had to chose then the LS3.
True!If you want an LT1, then you can buy a '93-'97 Z28 for what it would cost you to do the change over.
only the steering rack, front springs, and sway barsForgot to add, if you buy a Z28 you are also getting the better suspension.