First, just because your bike overheats, that doesn't mean the plug will be white. A white plug tip indicates a lean condition, while a carbon fouled black tip indicates a rich condition. Neither of which tell you much about weather the bike overheated or not. If you see small little specs of silver stuck to the plug tip, that may be an indication of piston meltdown. But, if the skirts, and cyl. wall look good, you will have to go deeper to find the problem.
There will be some play in the gears inside the clutch cover, an owners manual should indicate specs for this. As far as I remember, the kickstart gear rides in the right case, and the clutch cover, so it's is going to feel loose if the cover is not in place. Some of the other gears also ride in the clutch cover and will feel sloppy until they are held in place by said cover.
I think you better pull the head and cyl. off and check the top end bearing, and the bottom end bearing and see if that is the source of your rattle. If they are ok, keep looking deeper.
As far as I know, you have to install your ring gear on a new Hinson basket. I've only done three in the past though, all on YZ's, so that may differ with other brands.
YZ165