The full round FA was a subjective cost-saving decision made after-the-fact and after all the A2 testing we did had been completed.
Obviously we were in error here and the several thousand that had been installed replaced.
Funny, we made the increased diameter/strength lower receiver (buffer tube area) decision at the same meeting but never though about the two being incompatible.
Then later, the Army at Rock Island made the next cost-saving POS decision and made the plunger head too small.

Morg, you asked:

"...
All right Sir, you've stepped in it now.  I have two questions - IMO the early unmodified large head FAs are rare - so I'm thinking it might not be a good idea to modify them, although I'm sure many were, although I'm not sure at what level that would be in the Marine Corp structure. I'm guessing as low as Company, but not sure how Gunnys are distributed in your system. Some clarity here would be appreciated...."

I would modify one if making a correct very early issued A2, as about 2,800 were delivered like that.  But then they were changed out with the correctly designed flat sided, large head plunger assemblies for some X amount before the change to the now ubiquitous pos small head. I believe this replacement would have been done by Contact Teams from 3rd Echelon Ordnance Maintenance units. The original plungers then most likely went to the Base Surplus outlet, as I don't think it would have been cost effective to send them back and forth for modification and refinish, etc.  The photo above of the unassembled plunger heads is interesting because it represents how the logistic system tries to have repair parts in the system for repair/replacement even before a new system is fielded.  That was part of Rock Island's job, and by then I mean Mr. Loren Brunton. I mean this anomaly was first noted during the Division Matches at Quantico with the initial rifle delivery there to Weapons Training Battalion, i.e., before fielding the A2 to Line Units, or what we call Fleet Marine Force (FMF) units.

'...
The second question is, How essential do you consider the forward assist, and how do you feel about its potential for misuse? (SPORTS specifically.) I'm sure you're aware of the much quoted line stating Seal Team Two's opinion that forward assists were unnecessary. I'm definitely not a believer in them myself, and am a 'heavy lube' convert myself - would love to hear your views on this..."

The FA was added by the Army because even the officers, as well as all the Soldiers at the time, had the M1 or M14 Rifle muscle memory of hitting the rear of the operating handle to ensued the bolt was fully forward when loading. When I was M14 armed, I religiously did this thousands of times, but never once did the rod move any further forward as the bolt was always fully forward and locked for me--even though thousands of these loadings were with blanks.  Mr. Stoner told me many times that the Army's FA was not necessary and would cause more/worst problems than it cosmetically solved.  However, if one did inadvertently ride the charging handle home, I guess a push on the FA would be prudent, but you can accomplish the same 'check' with thumb pressure on the bolt carrier. And secondly, if one re-tracks the bolt slightly to ensure a chambered round, then using the FA is to ensure the bolt is then fully locked is prudent.

I don't know.  One would have to have access to the drawings Colt used or released to prospective vendors to see what degree of variation was allowed.
When I get home in the Fall, I'll compare the one I have with the photo.
Here is the D shape one I have.

Albeit, left-handed like me, but here is an alternative use of the FA recess....