i suggest u to go for engine swap go for margalla 1.3 engine i dont know about expenditure but not a days there are a lot of engines in market people are swaping in khyber.its original engine give 12km/l while 1.3 give 14km/l + more pick and power
and even u can go for g10 efi cultus engine which will be costly project but gives u 18km/l average
2 years ago my khyber engine overhauling costed me around 30k