Plenty of room for a 991 on the bottom. Note at the rear of the ramp with upper 911 the triangular structure from the tower to the ramp. If you put the 991 up top and have rear 305 tires, you will have only an inch or two of clearance between the triangles that connect to the ramp and the towers so once I am on the ramp and just before the rear wheels approach the rear towers, I hop out and do a quick clearance check. Only an issue with the narrow BendPak lift.