Hello Cuza ,
IMO the CR-1020 is a very nice and valuable vintage Yamaha receiver, it's not a good idea to start modifying it to make more power.
If you want to experiment with amps you better get a kit to put together and modify to your liking.
Of course it is yours and you can do whatever you like with it, but I don't think many people here are going to support you with that.
Now if you decide to restore it to like-new condition (recap, re-lamp, de-oxit, clean-up...) then you are at the right place here...