I am very sorry must have missed these posts. Will try to answer them if it is of any help now. Sorry for the late replies (blush)
G-15 is going strong and great Mash'Allah really enjoying it. Well my daily commute is on Islamabad Express Highway and I'll term it as semi highway drive. Following is a pic of my last 5 fills. These are during literally in stop and drive traffic due to the Metro project. On long routes I get 18+ kmpl with speeds of around 100-110 km/h. With speeds above 150 km/h got an average of 13+ kmpl.
Performance of the car is good enough, a good pocket rocket. Never calculated the 0-100 timings but it does ~95 km/h in 2nd gear and ~155 km/h in the 3rd gear suffice to say it is pretty quick and fun Top speed I am guessing is ~200 ? 10 km/h. Since I've a lexus' meter so can't say for sure.
AC was not installed due to budget constraints but will go for it tomorrow insh'Allah. Will update the thread when its in.
If the aim is not a power increase then in my opinion it would be better to get the engine overhauled on company specs instead of the swap. Khyber's original engine is pretty good and gives good mileages if overhauled properly and it isn't underpowered by any means I used to take my G10 upto 140 km/h on CNG and the acceleration wasn't bad either. A swap is feasible only when looking for a significant power increase I think.