As has been said only early evos had the ali doors (mine did), they made the 3.0 GT M3 (all in green with a different spoiler) as an end of line get rid of what we have left deal and to make it more desirable, the ali doors gave it less weight. The left over doors were used in the first lot of Evos
also the single vanos 3.0 has only one throttle body where the 3.2 dual vanos has one on each 6 cylinders. Also the 6 speed box in the evo is a give away.
The 3.0 didn't get the "Vadar" style seats and I think ther were some differences in the centre console vent (one big one instead of 2)
The evos never really hit there quoted bhp where the 3.0 did and sometimes even produced more. The evo with its 6 speed box was faster and had a better top end but it was all much of a muchness
People tended to go for the 3.0 due to the fear of vanos failure which was a little bit exagerated but a genuine concern (mine had a change out before I bought her). Regular oil changes and vanos filter changes helped
Easiest way to check from the outside is the reg

although there is so many 316 with m3 kit on them I was glad to get an e46 also as my mate found out on mine along with other m3 owners pikies like to strip bits off your m3 for their 1k piece of crap to "m3 it up" gits
Amazing performance with no waiting for vtec or turbo lag, an astounding chassie with top notch feed back. Far better to drive performance wise than the e46 M3 but not as comfy (if that matters) showing its age and to common and prone to "losing" bits off of it
A true classic