I will +100 on Mike at Dtech even though my .243WSSM upper came from Accuracy Systems. (nothing but good stuff to say about AS either though)
OlyArms can most likely get you an upper in the non-heavy version, but most likely NOT the pencil style. The wait at Oly will be less, than Mike or AS, but in any case...good luck finding them in stock somewhere.
I'd actually recommend considering the .25WSSM due to the larger deer bullets you'd be able to sling. getting much over the 100gr in the .243WSSM are tough to come by, and reloading them properly makes fitting them in the mag an issue.
I would suggest the WSSM AR15 version over the AR10 .243Winchester version, due to performance...but the AR10 version gets points on ammo availability and options.