71 340 AIR CLEANER PAINT

This may or may not be of any help, but I have read that sometime in the mid-'71 model year Ma Mopar switched from wrinkle finish to satin/semi-gloss black; which could explain why we see "original" examples in both finishes (They may also have been using up remaining '70 inventory, which was wrinkle). If this is the case, if you have an early production car, paint it wrinkle- if it's late production, semi-gloss. No idea on a date of the cutoff.
For what it's worth, the last '70-'71 air cleaner I had (way too many years ago, and it was original finish) had a light wrinkle finish- way lighter than the usual heavy VHT black wrinkle.