A number of years ago I built my motor and installed the clutch and PP then covered the motor up and left it for a couple years. At some point I pulled the bell off as well as the clutch and noticed where the metal particles are in the disk it had formed rust spots on both the flywheel and PP. The motor has been stored in a VERY dry environment so I don't suspect humidity or moisture being the issue. Anyhow., I'm now about two months away from installing it in the car BUT it likely won't be on the road till the summer of '24. So basically my question is: has anyone else experienced this problem with long term storage? Its a Centerforce dual-friction assembly.

Many times. Some sort of moisture got in there. Pretty hard to stop that unless you are is a controlled atmosphere. I would just sand it off.

My old clutch would "weld" itself to the flywheel over the winter when stored in the garage. The new clutch doesn't seem as prone to doing that.

I've seen front disc brake pads do that, stick to the rotors, on cars that sit a long time between being driven

^^^ Yup, discs and drums will do that if they sit long enough in the wrong environment, as well as clutches.
Since the engine's out, should be easy to pull the PP & clutch and clean everything up.

It's a form of Mechanical Welding that occurs. Metal pressed together under certain pressure.

This isn't the issue I'm facing. I already did that a few years back and left the clutch off. Now I'm in the process of assembling everything to go back in the car. BUT its still going to be sitting for the better part of a year while the whole thing goes back together.

Anyhow, I was more curious if it was a common issue. I'm well aware of what brake pads and rotors do - my wife's bitching about it all the time on her car !