The Imp Officer and AT-ST Driver (and many others) actually sit on a post. More of the headsculpts actually were postless than not, if I'm not mistaken. Just if you're curious on that Matt.
I actually customed vintage stuff LONG before the modern line even existed. I did the Hoth Trooper headswap too but was never that pleased with the outcome as the officer's more white than the trooper's "white" parts of his uniform, if that makes sense. It's definitely one of those "first timer" customs I think a TON of people did though.
Anyway, onto the actual figure...
-I LOVED the vintage Hoth Rebel Trooper. Even as a kid I liked army building to some extent, and these guys wound up being GI Joe grunts in cold weather gear. I'd get them for like $.10 at flea markets and garage sales way back. It's still one of my favorite vintage figures...
I wouldn't even consider the Derlin figure to be in the running for the Hoth Rebel... Much like Hoth Han's coat, they just got the color wrong on the trooper's "vest" bits. He's clearly based on the Luke-ish uniform. Derlin's uniform is a is the cold weather equivalent of Capt. Antilles' uniform, or General Dodonna's briefing short coat, and so on. Riekean's basically the same deal. They're the coats of the higher ranking officers.
Luke's uniform (and that of the source material images Scott provided) I always felt was a cold weather equivalent of the "Honor Guard" styled uniforms. There's actually a couple of those on Yavin, and they're distinct and clearly intentional variations on the uniform (one's more fitted and "proper" looking, while the other is looser and baggier). I've always then considered Lukes to be likely something of a lower tiered officer or separate branch of the military perhaps.
It's easily on eof the cooler and unmade designs, so I'm really hoping to see Hasbro knock this guy out of the park some day. The name "Echo Base Trooper" has always worked well since those cut scene images of them battling wampas surfaced years ago. I'm really anxious to get this one from Hasbro though. Definitely my top ESB want at this point, actually.