96 vortec 305 to 350 swap

Has anyone swapped out their 305 vortec with a 350? I have a 96 Ext. Cab and would like to put a 96 350 in it. I bought a wrecked 96 that is complete except for the computer and a couple of sensors. I thought I read somewhere that only the computer needs to be re-flashed at the dealer - is this true?
Thanks