You don't need any one to validate your public image on this site. You asked:
Could I just weld one on?
I replied : Yes If your just going to cobble/weld something on there so you can ride the bike I suggest that you measure that shaft stub and weld a go cart clutch on it.
Had I known this was going to be your mode of supplementing your livelihood I would have backed off : Head in another direction my friend. Wish I knew more about Heros now.
Do you even have the means to do the welding?