I did mine without taking the engine out of the frame. I used a Clymers Manual as my guide. I didn't think it was too hard. I will say that I did some other work recently and chose to remove the engine from the frame. That also was not too difficult. Just be sure to disconnect all the wires and remove all the mounting bolts and brackets. I got stuck on that for a few minutes when I pulled mine out of the frame. Once it is out and on the bench you would be surprised how easy it was to work on. If you are just doing the chain I would probably leave it the frame though.
Hurry up and get it done, warm weather is coming.