So, I got the engine out of my RX8 and am planning on going ahead with a REW swap as the irons/housings aren't in amazing shape and I'd like to learn a little more about them before I do anything, which could be months.
I've heard these flash rust really really easily so I was wondering what would be the best way to preserve these long term without any damage?

 

I coat my engine parts in either WD40 or engine oil depending on the part, before I store them. I typically coat irons, rotors, and the eccentric shaft in WD40 and wipe the chrome on the housings with engine oil.

 

There's a product called Rustlick we used in our machine shop to keep parts from rusting while waiting for assembly.

 

^^this, and keeping them in HD plastic bags like they come with from the factory helps keep stuff from getting them dirty.
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Go to parts store, get a spray can of cosmoline.