Luke, have you finished this yet? If not, as the guys above state, remove the cross member...it's only 8x bolts and a bit of 'encouragement' to release the crossmember + gives you a chance to clean chassis and jet wash out and treat the crossmember before putting back in.
I've just done my Def 200tdi and the only fiddly parts are 1. the downpipe bracket to engine screws [especially the one next to the engine mounting], and 2. getting all the exhaust mounts and rubbers to sit correctly. For best fitment, attach the whole exhaust loosely, then from manifold onwards tighten up rearward to have an unstressed exhaust. Good luck...