Ok dude, you've been led wrong somewhere.
First of all, the Probe GT motor is called a KL-DE, it is a 2.5L A-spec motor that is chosen over the J-spec version (KL-ZE) due to its lower compression ratio when the tuner is planning on putting a turbo or supercharger. The KL-DE has ~160hp and will bring you into the high 15s in an MX3 if you do it right.
The KL-ZE (2.5L J-spec) has 197hp and can bring in times around 14.7 seconds stock. Exhaust, intake, pulley kit and some lightweight will get you down to around 14.4-14.5
Both of those motors are V6's and if you plan on swapping a 4 banger to a V6, you better bring your chequebook. A lot of part swapping is involved fot this particular swap, and isnt recomended.
If you're buying a 4 Banger, your best option is a BP or BP-T. I dont know a lot about these motors, but if you read up on
http://www.mx-3.com in the FAQ 4-Cylinder section it will help you a lot. A BPT swap usually costs around 3000-4000$ from what I have heard, and will give you 200hp (mid 14's).
IMHO, the only way to get your MX3 into the 12s is lots of boost, or a serious diet (Im talking not even a cigarette lighter serious
). 12s will cost you a pretty penny. Unless you're retarded (Just kidding Steve) or willing to spend ~8-10K, forget F/I on a V6 MX3.