Have you checked or replaced the steering bearings? Are they notchy or self centering with the front wheel in the air? do you feel hear click/clunk when the front brake is applied when riding?
You have a few things that may make it more likely to shake, the front fender also acts as a fork brace, Yamaha used a piece of steel inside the fender to help stiffen the fork. That front tire looks pretty big for the rim. tall and narrow is less stable than fat and short.
You have a few things that may make it more likely to shake, the front fender also acts as a fork brace, Yamaha used a piece of steel inside the fender to help stiffen the fork. That front tire looks pretty big for the rim. tall and narrow is less stable than fat and short.