Well, that may be. Admittedly I only spent the entirety of my twenties and some of my thirties taking or teaching courses incorporating small unit tactics, and employing them in both training and operational environments. So I could certainly be all wet on this, but whether the candidates or soldiers were armed with SKS or ARs, or even No 4 Mk 1s would matter not one whit, only the weapon specific portion of the instruction would change. And I suppose, "change magazines, fix bayonets" would have to become "charge magazines, extend bayonets" if you had SKSesssss. Seriously, if Red Dawn happened tomorrow and I found myself leading a section of guerillas (aka fantasy world where you get your pick of rifles) I'd take my Sako 85 Black Bear in .30-06 just for the LCF, and poops and giggles. That's how much it really matters. Also, the protagonist in Robert Ruark's "Something of Value" carried a .416 Rigby bolt gun during the Mau Mau uprising, and I always thought that was as cool as sh*it.
Section battle drill hasn't, in fact, significantly changed since the advent of the LMG into the rifle section, which is where the real firepower comes from, and the Canadians were using bolt action rifles at the time. A Canadian rifleman from WW2 would blend nearly seamlessly into modern infantry section and platoon tactics, though I'm sure they'd marvel at the LAV III. The basic battle drill, truly, has not changed since WW2. The seven infantry section battle drills of Prep for Battle, React to Effective Enemy Fire, Locate the Enemy, Win the Firefight, Approach (and here's decision time, you have two big choices; frontal or flanking. Well, three I guess if you count left or right flanking as two separate choices), Assault and Consolidation would be as familiar to an infantryman in Normandy, 1944 as they would be to one in Pashmul, 2006.
That's not quite correct, at all. There seems to be some conflation here between tactical, operational and strategic doctrine. The US did overhaul it's small unit tactics POST Vietnam, but certainly not during or upon adoption of the AR. The key changes post Vietnam were the codification (in FMs) of patrolling, ambushes, etc (in other words enshrining the lessons learned from small unit fighting in the jungles and paddies) - but most specifically the changes that came with the adoption of a true LMG, the M249. The cornestone infantry section and platoon manual used during the Vietnam war, 7-15 Rifle Platoon and Squads, was revised just prior to the initial introduction of the AR, and nearly two years prior to the adoption of the XM16E1 as the M16A1. The M16 most emphatically did not drive either small unit tactics or larger operational or strategic doctrine, the nature of the war in Vietnam did.
The terms used above (momentum, set piece engagements, etc) are a bit confusing to me - they resemble but aren't quite the "kosher" terminology I'm used to, so I may be misunderstanding what you mean. If so, forgive me... That in mind, the US Army has absolutely not maintained or expanded on the same doctrine since Vietnam. The doctrine adopted immediately post Vietnam was called Active Defence, and was still attritional in nature; that is, it emphasized manoeuvering to bring fires to bear. By 1981 - 2 it had changed again to AirLand Battle, and was the first manoeuver warfare doctrine the US adopted - that is, it emphasized bringing fires to bear to enable manoeuver. AirLand Battle has itself been replaced by Full Spectrum Operations and Network Centric Warfare.
As mentioned above, the keystone FM relevant during Vietnam was FM 7-15. It was replaced by FM 7-8 which was in use from the mid 70s to 2001, and the current one is FM 3.21-8. If you delve into them and compare the tactics, you'll see that it really wont matter in the slightest if the rifleman concerned is armed with an AR, SKS, AK or for that matter a K98K.