Rob Gronovius
I thought the original had a single M85 .50 cal machine gun and the updated cupola had the 40 mm grenade launcher
Yes, there wer all sorts of variations, IIRC. The big change, again, just from memory, was in adding the second, weapons cupola.
The USMC AmTrak Companies did not field them, uniformly, either. The Landing Plan had to cope with distributing the "grenadier" versions out equally among the assault elements.
Which was tied into the Commander's Intent for how many of the tracks were menat to continue on as APC, past the littoral, and how many were to be retained for shuttled supplies ashore. Which was often due to the geology between low water and high water. If the ground above high water wanted tracked vehicles, you migh keep them to traverse supplies.