Does anyone know how much torque this thing can handle?

How is it constructed and how could it be uprated?

On a 340 its not the bellhousing thats fails but the propshaft but with good alignment and a good prop about 150nm is about the most to be relable and uprated would up that to the gearbox limit of About 300nm if you dont drop the clutch from a dead start

If you are modifying with a FWD engine I think you need a pilot bearing at the end to capture the clutch shaft, otherwise driveshaft alignment is the biggest issue.