Getting the OEM US Spec down pipes out can be a real PITA with the transmission in. You should not have too much problem with the top bolts on the driver side if you use an extension with a universal or flex socket from the bottom. Be sure to start the top bolts by hand so that you don't cross thread them. After you get them started put the nuts on the bottom studs because once you start cranking down on the top bolts you may not have enough clearance to get the nuts on there.