TRD does not make Superchargers for 20V, and do not listen to @palay regarding lowered springs or shocks. Coz if it is GT version as you say it is then it comes with a better spec suspension then your normal JDM rolla.
And do listen to @Palay regarding the exhaust manifolds, but do get good branded ones. As for the intake either get short intake or go with the Individual Throttle Bodies, it is like installing a Supercharger on the 20V. get a ECU upgrade to handle the fueling better.
you can go to the following sites for better understanding to what else can be done, but do not be limited to them
http://www.billzilla.org/ae86stockpage2.htm
http://www.geocities.com/MotorCity/7177/tech.html
then there is club 4age and toyota nation.