Remember to bang a bit engine protection pan where header may contact it. You don't need rest of bushings mentioned like tranny/diff/subframe. And if those mentioned, remember that with all of them installed NVH will noticeably suffer. If one installs just one less compliant bushing somewhere, vibrations/noises can be passed to other bushings up or downstream, reducing impact to NVH. If all bushings are non-compliant ones, all the noises & vibrations & rattles are passed to you
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I don't have ace headers, just wanted to tighten a bit suspension & enhance gear shifting feel. Rear subframe inserts did nothing to NVH, tranny mount & rear bushing added slight gear whine at 1st & 2nd .. but when i added diff bushings & engine mounts to those, i hated result. Gear whine was much louder and now audible in other gears and on car jumps on road defect gearbox rattled a bit, clutch got noisy and awkward to use (due driveline shocks passed now to only springs in it), extra noises from engine vibration .. reverted to just gearbox mount & bushing & subframe inserts. In same way you may leave engine bushings for header, and maybe subframe inserts .. but i wouldn't go all the way changing out all possible driveline bushings. Result might be not to your liking.