Interior
I fabricated some custom seat mounts
for my Sparco Seats (Corsa driver,
EVO passenger).  I wanted to make
sure the connection between seat and
frame was as good or better than
stock.  The stock mounts/electric drive
is almost an integral part of the stock
seat so unless you're willing to ruin a
good set of seats making new mounts
is required.  There are some
aftermarket manually adjustable
mounts you can buy but they appear
to be a weak link to me.  My mounts,
machined from 6061T6 are adjustable
but it takes about five minutes to
remove a couple of bolts and make
the change.  A bit of a pain but a
small price to pay to the knowledge
that my seats and body with remain
firmly attached to the car in the event
of a major rollover.  
AIT and oil Temp gauges replace the
location of the stock stereo system.  No
big deal, it saves weight and I added a
micro connector and switch to work with
my IPOD so tunes are no problem.  The
little thumb switch on top of the shift
knob is for "blipping" the throttle.  I
connected it to the stock cruse control
and when pushed holds the engine RPM
steady at whatever RPM I want.  This
help synchronize the gears during
downshifts and helps smooth the
transition thus reducing unwanted
chassis disturbance when going from
hard braking to acceleration