bro first choice will be to overhaul this machine
but if its done 2 times before and engine is already bored ..... then swap is must
as far as cultus is concerned
you will get old 1000cc 3 cyl efi version in market as well that costs round 40 to 50k ... most of them are japan imports
1000cc 4 cyl local engine wont be available in market ..if you get 1 will cost 80k to 90k
i would recommend you going for K6 660cc efi engine
atleast these engines are new .. have parts coming in market and good power n economy