I used 2" thick closed cell polyethylene foam sheet from Grainger for its water resistance. It's easy to cut into strips but not very compressible so took a few tries to get them just the right size. Grainger has other foam material options if you want something more pliable.

Ok just did mine with an N-flo koyo on a JDM FD. Omg I hated everything doing this install. And so pissed I bent some fins during install. Long story short, my bottom brackets were still good, allergic I bought spare, since first time up nothing fit... fuse box, smic, etc. But I went back and flipped that AC bracket and it didn't flip radiator brackets and it worked. I didn't try without flipping Ac with unflipped rad brackets, because I was already annoyed. Needless to say my ac bracket needs modification to bolt in because it wont line up with screw maybe if a mate held it down it might work. But i zipped tied it until I have patience to take apart again.rad is in. Bleeding air. Taking forever but yeah