Replaced the turbo 350 in my Camaro for a turbo 400. Do I have to replace the shifter linkage? Don't know if the 350 and 400 shifter linkage is the same. Thanks!

 

I think the shifter linkage will be ok but the T-400 has an electric kickdown for passing gear so you'll need those parts to replace the cable kickdown on the T-350.
You'll need a different yoke and driveline or mods to it as well.