2009 TE250 Cylinder Head Overhaul

After the ever worsening rattle, I bit the bullet and took out the engine. The cam bearings are done for, but I still wanted to check the piston / bottom end. The mileage is approx. 4,000 but the barrel is Athena 300cc, so the B&P are lower mileage than that. With the head and barrel off, the barrel wall is smooth, piston looks good and no issues with the crank. Questions:

1. There was some swarf in the cam box on top of the head and a little in the front LHS strainer. Am I going to be OK with the bottom end and how best to clean out / flush without dismantling. Oil was clean - no metallic sheen - guessing the swarf is from the worst of the cam bearings, which didn't look like it had long to live.

2. The rear external head stud nut was solid. This has really limited access, so I had to get the dremel on it. I've damaged the stud as well. Are these OK to get out or will I need to get it to a machine shop?

3. There's some oily residue on the piston top and the combustion chamber. I'll strip the head now and check the guides. One exhaust valve is white. No idea about this, see pictures below.