I also have never seen the spiked version, only threaded. I went through the early GM part numbers for speaker covers, none were unaccounted for, if that means anything.
http://i552.photobucket.com/albums/j...oa1/2f04_1.jpg
While the general oval shape and stamping is very similar to the common '72-81 version, I haven't seen one with the speaker holes closely following the speaker shape with no holes in corners.
https://i.ebayimg.com/images/g/iu0AA...3y/s-l1200.jpg