change the sprokets, get the old piston out, get the chamber bored and put a new bigger piston like say of honda 250 of police bikes. add disk brake to the front. if u wannt to install a new wider tire, u';ll hav to widen the length of the rear swing-arm and suspension to fit it. make the front forks more declined in angle like 5-10 degreess more to giv it a classic hog look. add a new exhaust pipe. it can easily be made from any heavy bikes mechenic shop. they can custom made it for u. Since it has 2 cylinders so it will be a simple but custom made 2-into-2 or U can have 2-into-1 Xhaust to ur specifications like give it a slashed tail look like kawasaki eliminator series or u can have long tail pipes like harley fatboy 1200. redesign the fuel tank as the present one is too lame. have some good fabricator design it 4 u..believe me everything is done in Pakistan and mechenics here r very well talented and know their work. u'll have to invest a hefty amount of time in modifying ur bike.
im posting a few pics 4 u sodat u can get the idea of modifications xteriorly.