although its an ancient post, but still we have to share our experiences(H)
kei is a very good 660cc car, as the wheel-base of this car is the same as ALTO(VXR 1000cc), therefore 80% of maniacal parts are readily available(even from suzuki).
as far as engine is concerned, its absolutely perfect, just keep it maintained(regular oil,filter changing ETC) , it will run smooth at-least for 100000km(can`t say more as i have driven it up 997k yet).
Please do not install CNG, specially in turbo model.
better opt for non-turbo model even in petrol.
body parts are also available in the market 99.99%
it has very good pick, i use to travel regularly from Murree to ISB, "it never let any mehran get closer to it"(tested on journey from ISB to naran:P).
if you keep it well tuned , than its 15km/liter local and 18km/lit on long(if you keep it within limits)
it has a great advantage of 4th gear in auto transmission(most 660cc have only 3 gears-FWD).
last but not the least, its engine is also K-series, so due to arrival of wagon-r ,engine parts won`t be an issue.