Dude, I'm in your boat. I have a proportionately larger torso and head than the rest of me. However I have managed to sucessfully handle everyone I've fought--shittiness of local fighters not withstanding.
I don't know my arm length but I'm 202 with arms too short for my body, or for anyone else's. Meaning I'm well within most of my opponent's reach before I can tag them with a solid cross, or even with a decent hook.
Its brought on an advantage in hind-sight. The need to get in so close has done wonders for my guard as well as with my aggression and accuracy. I know that I have to have a total picture of my opponents helps with my choreographing and anticipation. I've even in one case managed to react to an opponent before he even acted. But he was easily choreographed--and really bad.
All in all, body proportions mean nothing. You find your niche as you continue to train. Your strengths come out early and with focus you can be whipping asses in less than a year--depending on effectiveness of local fighters.