Rosanne, here's the deal. The original block is probably made up of mostly HSTs, with a couple of solid squares towards the middle.
If we were to use our exchanged reels, they would need to be trimmed down to something less than 3-1/2" x 3-1/2" because the closest "regular" size HST to work with our reels would be 2" (finished size). If the reels were cut down to exactly 3-1/2" x 3-1/2", they would actually need HSTs that measure 2-1/8" (finished size), and that's not something I would want to fool with!
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If I were actually going to make this quilt with our reels, I would paper piece (using Edyta's papers!) 2" HSTs for the outside units, and paper-piece the reel and 4 triangles in the middle as a single unit. I hope someone does this! It's a cool design!