The 931 is a 924 turbo. The transaxle is basically an AUDI 016 but does not have the provisions added for using a clutch. The input shaft isn't machined for a pilot bearing either.
The "dogleg" transaxle was used in the 80 US and 79-84 ROW 924 turbos. It is a much stronger transaxle than the 016 but probably wouldn't work very well for mid engine. It uses many Porsche 915 internal parts. It has the diff behind the transmission section and has no bellhousing. It attaches to the 924 torque tube with 4 bolts that are approximately in a ~4" square pattern. You would need to adapt it to a bellhousing and make up a shaft to extend through the clutch to the engine.