Some details, the 270 might look like it has more webbing inside the bell, it does but has much less on the outside.
Look at where it flushes with the engine, the 310 is solid where the 270 is hollow.
Not sure if this is the only difference but it is as to physical on the exterior.
Both use a 10" torque converter and have the identical output shaft. All seals and parts so far are identical to the 4l30E except the big trans pan, these do take BMW specific shape gaskets.
I will update if I find anything else different.