Say that a man was nearly seven feet tall and weighed over three hundred pounds, most of it muscle. Would his height and weight just be a pain in the butt given the standardization of gear and accomodations, or are there any specialty niches such a person would be ideally suited for? Maybe a real-life “heavy weapons dude”, who could manage firearms with too much recoil for a smaller person?
Pain in the butt and while I don’t know the numbers offhand I know seven footers won’t be permitted in several of the branches because there is an upper limit on height.
From here, the Armed Forces in general won’t accept you if you are over 80 inches tall (6’8"), and the Marines won’t take anyone over 6’6". So the answer appears to be no.
I will say anecdotally, most of the really big military guys I have met have been infanteers, and some excel in areas like survival training and the like.
They shy away from armoured (vehicles can be cramped). Some go arty, but by and large, most are infantry.
This is strictly anecdotal. The tallest I met was about 6’6" and he was a machine gunner.
An Australia soldier who recently won the Victoria’s Cross is 202cm tall, or about 6’ 7.5"
We send you in to infiltrate Castle Wolfenstein.
My partner, who is 6’10", was turned down when he tried to enlist around 1985. And I believe he was also disqualified for being underweight (for his height).
Big Guy = big target for snipers.
Big Guy = huge foxhole during artillery and mortar fire.
Just saying. 
How big was “The Swede” supposed to be in Clint Eastwood’s Heartbreak Ridge?
David Robinson was 7 feet tall when he graduated from the Naval Academy and that didn’t prevent him from going on active duty. Wikipedia said the service academies don’t enroll anyone over 6 ft 8 in, but they don’t discharge anyone that grows past that.
http://en.wikipedia.org/wiki/David_Robinson_(basketball)#College_basketball_career_and_military_service
Audie Murphy is the most decorated combat soldier of the WWII. Among his 33 awards was the Congressional Medal of Honor. He was barely 5’ 5". Being small in the infantry is an advantage. You can jump into any bit of cover. 20 mile marches are easier when you only weigh 160 lbs.
Big guys would be better on the flight line as a mechanic, or some other tech specialty. Radar, radioman, computers etc.
Artillery. Those big shells don’t load themselves, you know.
Too much muscle can actually be a bad thing in the military. It’s weight you can’t put down, and eats into your endurance.
Speaking of eating, they (apparently) only make MREs (or whatever they call 'em now) one size. One portion does not fit all if you have to cater to Hervé Villechaize and André “the Giant” Roussimoff at the same time.
(Yeah, both dead, I know. Imagine a zombie army making Brains Ready to Eat.)
This guy wasn’t bad either, and was 5’ 3".
There’s a saying that short guys make better soldiers because their brains are closer to their balls.
Gen. Washington himself said the Revolution might not have been won, had it not been for Peter Francisco, a giant: Peter Francisco - Wikipedia
MP?
The pumped up military guys that I see on the news and in photographs who are serving in Iraq and Afghanistan don’t look like the soldiers with whom I served. Or like the pictures of my dad and his comrades, for that matter. Muscle bulk like that was really uncommon.
Robert Renneman graduated from the Naval Academy by which time he was too tall for shipboard duties at 6’ 7’'. As a result, he was transferred to the army just time to fight in Korea. The account of what happened there is, among other things, rather touching.