SFI Specifications for Bellhousings are as follows:

6.1 Spec: For use on Naturally Aspirated vehicles ONLY; running SFI spec 1.1 and 1.2 two disk clutch assemblies, or SFI spec 1.1 and 1.2 three disk clutch assemblies  Commonly, Pro Stock vehicles will run this bellhousing

6.3 Spec: For use on Naturally aspirated cars running SFI 1.2 two disk or more clutch assemblies, or Supercharged/Nitrous injected vehicles running SFI 1.1, 1.2, and 1.4 Spec clutch assemblies, with a two disk maximum. Commonly, Pro Mod vehicles will run this bellhousing

6.2 Spec: For use on any vehicles running SFI 1.3 and 1.4 spec clutch assemblies. Commonly, Top Fuel and Top Alcohol vehicles will run this bellhousing