Removing the drive cage from the Silverstone TJ08
gives you unfettered airflow from that front 180mm fan. The case still has a 3.5" drive mount on the bottom (high-capacity hdd?) The fact that the TJ08 is one of the shallower (front-to-back) cases is one of the reasons it's so good for air cooling. Doing a simple case mod
of installing a 120-140mm fan mount in the top of the case (above where the 5.25" drive bays would sit) will give you even more airflow for dual GPUs... if needed.
Are you sure you need a completely passive system? Picking a good CPU cooler and quiet GPU(s) can leave you with near-silent operation in the first place. The two 120mm fans in the front of my case are the only thing I can hear from the system in my signature.
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod