you crazy? go out and buy a HDD and have both!! I could NEVER go back to a HDD system
Anyway - to answer your question.. yes.. you can clone your SSD to his HDD since his is bigger.
If he has more data on his HDD than the size of your SSD (I,e, more than 250GB) then you cant fit his HDD to your SSD.. you would need remove stuff to get it below the 250GB target (and realistically - it needs be a fair bit smaller.. you don't want it full).
You need an interim drive to move stuff i.e.
Move your SSD to interim drive
Move HDD to your SDD
Move interim drive to HDD.
You could do it with just your current drives if you HDD has more than 250GB free.. but it very messy - and beyond scope of this answer.
Anyway.. as I started out.. if you can.. just get an extra HDD and fit it into your machine as a second drive.
HTH
Cheers