"It seems possible that had the Western Allies decided to keep the German armed forces as intact as possible, and with a united front, Stalin would have been defeated in a head to head fight."
It seems possible, but certainly wasn't. It's not merely a matter of having enough men, tanks or planes, but of logistics and terrain, as well. Logistics and terrain are the primary reasons for German defeat on the Eastern Front to begin with, how you arrive at the conclusion that after their surrender there were a) any German forces capable of having another go at Russia and b) they would have been successful with American help, defies logic on many points.
Germany lost on the Eastern Front for three specific reasons:
a) Supply lines were extended and almost impossible to maintain due to distance, terrain, lack of security, and weather.
b) the German (really Hitlerian) predisposition to hold eveything they took to the last man, rather than engaging in tactical/strategic withdrawls when necessary, or otherwise conserving combat power whenever possible, in the face of determined Russian attacks, ensured that when the Germans tried to hold everything, they would, in fact, hold nothing.
The Hitlerian ideal of ensuring that every square inch of ground taken mby the Wermacht should be held by a German soldier and never relinquished guarenteed a lot of dead Germans in ultimately futile situations.
German commanders, acting mostly under orders or Nazi enthusiasm, frittered away a first class army in a series of stupid campaigns.
c)The vast Eurasian landmass simply swallowed the German Army whole. There would never be enough soldiers, in anyone's army, to present a coherant front against the Russian army under those conditions. This space gave the Russians a tactical advantage which they took at every chance they got; constructing defenses in depth, exploiting the gaps between German formations, slipping partisans and special units in to operate behind German lines, tying up front-line German troops in repeated security operations behind the lines.
Germany and her allies lost in excess of 5 million men on the Eastern Front (killed, wounded, captured and missing), and the average German soldier endured hardships, and experienced horrors, that had probably not been seen or felt since Napoleon's retreat from the gates of Moscow. There were a further million men lost just trying to keep the Russians out of Germany proper.
By 1944, the German army was reduced to culling POW camps for enemy soldiers with pro-Nazi "sensibilities" (The Freikorps)to be recruited into the SS. And that's when they weren't rounding up the children (Hitler Youth), the old men (Volkstrum) and the "stomach cases" (i.e. veteran soldiers declared medically unfit for combat duty, but still capable of at least dying, rifle in hand, in place).
The "German" trooops encountered at Normandy Beach were nothing of the sort, being mostly conscripted Poles, Ukranians, and in at least one circumstance, KOREANS (true story!).
There was nothing "to keep as intact as possible" vis-a-vis the German army of 1945. There were very few soldiers left capable of anythign except stubborn defense to the death.
As to your assertion that a "united front" would have been a deterrent to Moscow. Well, it was; It was called NATO.
Whether ther Western Alliance could have become NATO-like in 1945 (instead of '48)is another argument altogether, though.
From what I understand, Stalin had his own problems, in regards to the continued ability of the Red Army to maintain a high level of combat worthiness. I certainly hope you don't disregard that possibility in arguing for an invincible Red Army.