yes you could buy the complete cosa clutch already with the renforced ring art: 93031000.
When you have the complete cosa clutch it is not in your case a plug thing since you have told me you have the malossi upgear kit. This means, as I told you in my previous answer that you have changed the primary gear in your input shaft (christmas three) and now you have a malossi with 64 teeth that are straight. The cosa cluch use elicoidal teeth so you can’t mount it unless you change the primary drive of your christmas three or change directly the christmas three with a PX200 one.
Yes you can mount 21X65 on a conventional PX150 clutch in the reinforced basket (art:93220000), but you need to change your clutch gear with art:17800000 and again you have to change the malossi primary gear on your christmas three with a PX200 one.
Watever you are going to do you have to change the malossi primary gear on your christmas three or change the complete christmas three with a PX200.
In case you want to change just the primary gear in your PX150 christmas three (imput shaft), yes you can mount the PX200 but you would need to take the malossi one out and fit the PX200 with a rivetting job if you know how to do it.
It is definetly easier to change the complete imput shaft (christmas three) with a PX200 one, then yes you can fit the complete renforced cosa clutch art 93031000 and enjoy it.
tank you my knee is slowly getting better.
For the moment unfortunately I dont have any of these items that you need second hand.
Now I really think you have all the options…