Hmmmm, the tech sheet you linked says 2.02"/1.60".

This KD-912 will be easy on the wallet. You can use it to disassemble the heads as well as use it to change valve springs with the heads on.
http://www.mytoolstore.com/kd/kdengi13.html

You don't necessarily need shop air to change the springs with the motor assembled. Remove the spark plug, roll the piston down in the bore a little and fill the space above the piston with clothesline rope fed through the spark plug hole. Roll the piston back up to shmush (technical term ) the rope up against the valve heads and remove the springs.