I bought an NOS 3916654 off EBAY, and pulled the original 7752901 off my header panel. Note this came off the header panel, I did not have a trunk emblem because there was a spoiler added to the car at some time in its history. I'm not saying the 7752901 was original to the car nor a header panel emblem. It just occurred to me that I should compare the original vs the "Genuine GM" and although these are different part numbers they should be equivalent (other than age and patina). Original on top in pics.
My first impression was that the original was heavier, but they both weighed 1.25 oz.
The original script has more distinct lines. The flat area on top of the script has crisper edges.
The original script has more angle from front to back of the emblem, which fills the space between the letters and corners. For example the top of the m has less open area than the new part.
The original "BY CHEVROLET" is blockier and crisper. For example the O is fuller.