mate u have plenty of choices like
G13B:- 1300CC, 8V ,4cly ,carby,SOHC (margalla)
G13B:-1300CC ,16V,4cly,Efi,SOHC (baleno)
G13B:-1300cc,16V,4cly,Efi,DOHC (JMD swift,cultus)
G16A:-1600cc,16V ,4cly,EFI,SOHC (baleno,esteem)
i dont know the local cultus engine code so that is an other choice
same goes with Alto engine .....i can go on and on in suzuki engines but they are wast for u so u stick with these ....
if u want it for CNG then i will say install margalla engine as its power is nice and it will give u good millage on CNG with AC and its parts are less expansive then any other engine i mention above and above all it will go straight in to ur engine bay with some or no modification as some JMD swift have G13 in stock as for cultus engine man its 1000cc and its power much less then margalla engine if u want power with economy then margalla engine is for u and if u drive ur car on petrol then i will say G13 DOHC is best but it will not give such good response on CNG so now its up you now what u want