Hi! Nice project! I noticed, nobody mentioned your fusion distance at 0.3mm might be far too low. The car parts usually consist of smooth surface with not much of surface details on their own!
The closer/lower the point fusion distance, the greater the file , fusion times and muuuuuuch more RAM needed.
I saw some great results with scanning body parts usinh fusion settings in the range of 1.0-1.5.
e.g. here Revopoint Trackit Volumetric Accuracy and Repeatability tested (with real-world examples)
Notice: even the points are farther away by choosing higher fusion distance , each point keeps the accuracy! You sjould get get a very nice smooth surface by bumping up the point distance when fusing because you reduce the “noise” ,too.. When doing the CAD model afterwards it should give you an accurate, even cleaner looking surface. You can DM me ,if you want me to do that one of these part for demonstration purposes - for free.