When I had my engine apart, I examined the head and intake ports to see if I wanted to do any port matching. I found them to be reasonably well matched one to the other as measure by eye against the gasket as a reference. Definitely not perfect, but imo not worth the extra work. I did find the exhaust manifolds to be mismatched and spent the time doing a port matching grind and polish using first a die grinder followed by a dremel tool. While doing that, I also over-cut the exhaust manifold ports to give them a little anti-reversion step - hopefully to give a slight torque boost, but primarily to make the engine smoother.

Certainly an exact port match will give an improvement, but without forced induction, I'm not certain how much of a worthwhile improvement can be gained relative to the effort and/or expense.

Headers might help (as noted by misterbishi), and in looking at the OE exhaust manifolds compared to what's on the Dianante/Stealth/3000GT, the potential looks more desirable for headers.

I'd be leery of changing the cam profile to longer duration until someone proved it worthwhile. Often, longer duration is the wrong way to go. Usually higher lift is what helps breathing, but it does vary with different engines and the learning curve can be very expensive. Many cams I've seen that give higher lift also increase duration and on some if you try to grind too much lift without extra duration you get more of a hammer/float action to the valve train which can cause a lot of damage over time.

What makes sense to me is to note what development changes Mitsu found to be best as they moved the 3.0L into higher torque/HP. They changed to 24 valve heads, but the torque peak changed. I don't know if low end was penalized or if it remained the same at 2500 rpms and kept building to 4000rpms. If anyone has the curve printouts it would be interesting to see them, because it might indicate that the later heads would provide a real highway driveability improvement.

To make more power, the next step was the DOHC change, which moved the torque back lower. The final step was forced induction. I think they've provided the clues to the upgrade path as they found it to be best.

Frank