Briggs 300 series valve questions

I'm currently working on adjusting valve clearance on my MTD push mower with a Briggs 300 series engine. The model/code is 09S502 0520 B1. This is a L head.

I had several questions at this point-

Is it ok to use a green scotch brite pad to clean the carbon off the valves and head?

I know the recommended valve clearance with springs installed, but does anyone know the specs without springs installed?

The intake valve was not very smooth when removing it, I felt a little resistance and noticed in the chamber there is a small rubber collar that is poking out. In the other chamber this collar is flush with the opening. Is this normal or not?

I have attached pictures. The first pic is the exhaust chamber, the second is the intake with the collar sticking out.

Finally, how freely should the engine turn? I feel like it's a bit firm when turning the flywheel and it stiffens as the position reaches top center.

Attached Images

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