well getting a big engine will require alteration in side walls which is not good rest is ok....
So any 1.0 will be batter
you can buy efi cultus engine for same price as daniyal said...so batter look for the suzuki stuff..
all i found alteration was of mounts position.....right mount point is same for my new engine.....the front position got changed and is now almost in middle of the front bar.....along with radiator ....same will go cultus engine
and 2 mounts on under engine plate which can be bought again....even if you make any chnages to it...so over all alteration is very low