Im 6'3 and 170pounds .... What size ???? and i've got preety long arms and legs.
A2 ... 5'6-6'0 and 140-170
A3 ... 5'10-6'3 and 171-199
You may have to mix and match ie A2 top and A3 bottom. I say order a Atama and call them and tell them your height/weight. I did and they told me what sizes to order.
Howard Liu at HCK is really helpful in terms of getting the right size. Also, I've been more impressed with the craftmanship of my HCK's than my Atama. Go with HCK's competition Single. You won't be sorry.
I wouldn't buy an HCK personally for your body type. I'm 6'2" 165lbs and my HCK is the right length on the sleeves but REALLY baggy around my wrists.
I'm the exact same size as you and I've only found two gi's that fit me worth a damn.
One is Atama size A3 (both gi and pants)
and the other is Keiko Raca size A3 (both gi and pants).
I actually really like the Keiko fits me perfectly.
Hope this helps.