Your frame is very similar to mine, big blocky chest, broad shoulder but long limbs which are difficult to put size on. I'm 6' and 232, I was measured for my kilt at 52 1/2 chest, 18 1/2 neck and 34 waist but my arms have never been bigger than18 1/2 - even at 250lbs!
Here's a good plan, a lot of people might dismiss it but it's working for me and it certainly worked for the guy I'll tell you about in a minute.
Get yourself a pair of push-up bars (see link)
http://www.powerhouse-fitness.co.uk/powerhouse-push-up-stands.php
with your feet, on your bed, do decline push ups every day, I do 5 sets of 30 throughout the day, except on chest day. I also use resistance bands to do curls, lateral raises, tricep kicbacks and upright rows, sets between 30-50 once a day. This, I've found, keeps a pump in the muslces and helps vascularity as well.
Right, back to the guy I mentioned earlier. He was an airborne medic, super fit (could run 1.5 miles in 6 1/2 minutes - try it!!!) and could bench twice his own body weight. His pecs were massive but the rest of him was in proportion and his bf% was always in single figures. The guy was a machine, he trained every day and, get this, won a competition in his unit (the old 5 Airborne Brigade, the British Army's elite parachute brigade) for the most push ups in an hour - 1637!!!
Don't knock them, they're awesome.