After searching 5,280 boxes in my house I finally found my Super System 4 tank (it's only a five-reeler, though). The reels are indeed 100% interchangeable.

No kidding- it was stashed in virtually the last box in my house I hadn't gone through! The five-reeler was there along with my faucet temperature gauge and my Dunwright & Vogel EcoWash... I had begun to think I actually tossed the items but if that were so then I **KNEW*** I was crazy since I'm a total pack-rat...