Sorry yar. i had a 2002 civic. totally stock only had 4tip bosch spark plugs.
i ran it till 2009 when had an accident n wrecked it by that time it had 175000kms on it.
it was always maintained by honda fort in lahore and it was a very strong car. pulled remarkably but dint have CNG.
150K per yeh haal hona may mean neglected maintenance.
as for Janleva.
i would suggest get an engine from a half cut car and put the same model engine in ur car.
that is the best way and do get it checked by a trustable and knowledgeable mechanic.
i had an 88 corolla. dad imported it for himself in 1992. we had it till 2013. we changed the engine 3 times n the car had run about 800000 with three engines.
as per my knowledge engine overhaul is mostly unsuccessful and takes a long time.
i got my 88's engine swapped in 7 days everytime. the third time one engine mount had to be changed even then it took 7 days which included old buttons connection with 2000 model corolla engine wiring, mount change and the swap.