Yes the '73 does weigh a little more , about 200 lbs., thicker sheetmetal . and yes you need to change the carbs to round top SUs . There are slight differences in the '73 from the '70------'72 but they are slight. If you are looking for a dragracer then that extra weight is a factor other wise I cant see any big difference. On any of the early Zs a good mod is to change to a electronic ignition . You can get one from the bone yard for about $50. If the car is clean and the price is right you cant miss. Gary Portland ore.