Not true Dave, the engine and nozzle are all installed with a down angle of a few degrees, not just the nozzle. It was a combination of reasons iirc, one being the need for the compressor end of the engine to clear the wingbox structure and another being for the jet eflux to clear the stabilators at the nozzle end and also to balance the thrust line with aircraft's c of g, as already noted by the OP. My memory on the subject is fuzzy however and there may be more pertinent reasons for the downward cant that I've forgotten...