What performance upgrades are there for the SOHC motors? What are you getting fuel mileage wise? And finally how many miles do you have on your protege?

I have had mine for 10 years, I got it from my Ex when she moved away for $600.00. The Odometer stopped working 4 years ago at 136680 miles, It is drivin about 20k miles a year, so doing the quick math thats216680 miles..... The car still runs great, accept for the heating up problem (i'll figure that out sooner or later). The car is almost completly stock accept for wheels, and high flow cat. The only things I have changed are the Brakes (pads, rotors, and calipers), clutch, timing belt (on the third one) water pump (second one), Fuel pump, and battery. Is there anything else I should be looking at as far as preventive maintenance? This is my DD, as I have 4 other cars, but none of which I would drive every day (too expensive), so I really want to stay on top of this car. I do not plan on ever getting rid of this car, it has got me through alot of bad times, so I have a major soft spot for it.

Now on to my plans for the car when it does die:
I have the drivetrain from my 98 mustang cobra sitting in my garage, and I have seriously been throwing around the idea of transplanting it into my protege, (I was going to build a factory five MKII) but i'm wondering how difficult this swap is going to be. Obviously I will be fabricating a whole front end, and cutting alot of engine compartment away, but I'm thinking the pro's are going to fall short of the con's... So at this point it is just in theory. Give me some of you thoughts.