well if you're talking about the 2000+ eclipses, i'd take ESCO's post into consideration.
well here's my experience with my lancer and a friend's 97 eclipse RS.
my friend has a 97 eclipse rs. modified exhaust section, short shifter, throttle cable adjusted to zero slack, and cold air intake.
i have a lancer OZ with just a short ram intake and muffler section. we did 3 runs. he beat me off the line by half a car and then stayed like that the rest of the way. all 3 runs identical.
and yes, the 4G63 has a wide aftermarket. the lancer doesnt.
for lancer parts available:
http://www.lancerusdmparts.cjb.net/
also this place is a good source:
http://www.rpw.com.au
it seems that they're converting a lot of 4G93(mirage engine) parts to fit the 4G94 (the lancer)
good luck