From the reddit forum he said to expect the 560 (3-slot) a week or two after release of 550. Here's also a handy breakdown to confirm your suspicions of the 140mm fan.
SM550: 2 slot, air cooled (2x 120mm fans)
SM560: 3 slot, air cooled (2x 140mm fans)
SM570: 2 slot, 240mm AIO on top + 2x 120mm...
Here's the ebay listing. Guy's asking $700 now. https://www.ebay.com/itm/NFC-Systems-SkyReach-S4-Mini-Buyer-chooses-powdercoat-color/183715938245?hash=item2ac652bfc5:g:1qIAAOSwF0VcHw6N&frcectupt=true
IMO, the listing is bogus. Calls out stock photos and 2-3 week to process. Guy is probably...
Sand, prime, first coat.
Finer sand, second coat.
Rinse/Repeat till desired finish achieved.
Apply top coat/gloss.
Sand, second coat.
Key is several light coats not laying it on like painting a wall.
Honestly I would look for a powder coating instead. My last case was a massive...