I did the swap auto to six speed swap on my is300, needed:
Standalone ecu, it will control your engine better, ignition timing and other engine functions will be tunned to your 6spd transmission. You will need the 6spd sub-tunnel, the 6spd transmission sits few inches higher, the 6spd sub-tunnel will clear the tranny.Shifter and related parts will be needed, the shifter linkaga etc...
You will also need the 6spd transmission mount.
You also should go with a new clutch and flywheel of your choosing that should be installed with the six speed. If you have an auto you have to have the supra rear as well otherwise your gear ratios will not work properly. You will also need a 5 speed clutch pedal and a slave cylinder. The subtrain on the rear needs to be modified in order to make it fit, need the supra axles etc.. You will also need to fabricate a custom driveshaft.