No. Stuttgart Auto will not entertain your request to bring in
or install aftermarket parts not officially approved or certified
for use on Porsches. They used to help install parts brought in by
the owners themselves until 2 years ago... the last car they
actually help to install aftermarket parts was on that Yellow 911
Turbo with the GT2 bodykit.
You don't really need to tune a GT3 since its already a beast
straight out of the factory 
The mods I've seen and heard here were just exhaust
and intake pipings and elements. Also came across a black MK1 GT3
that looked so stock, with wheels and all, but the engine was tuned
with hi-cam settings.
