82 250 Z engines start at 206697 so i would be saying thats what it is, but since the only information we have on 250Z numbers is that one number in the parts book, ( nothing else exists on the net on these) its best to check with your suzuki dealer if you want to be 100% sure, but i think you would be pretty safe to say its an 82 which are quite rare. Yes there are differences between 81 and 82 motors.
now you said an extra mount? extra compared to what? all 80-82 250's and 400's have the same 4 engine mounts.