Bob, if you are a new Anova user you should proceed slowly sorting with the basics of the technique.
Peruse the Community posts here and you will read of the many challenges to newcomers have with the app. Take Ember's advice and start manually until you have mastered the app..
Roasting is dry heat cooking. If you have had success with previous pork neck cooks you should do it again the same way.
I don't believe i know of a more challenging piece of meat to cook competently using the SV technique.
64.8C does't sound right.
You don't reveal if you have boned it, but likely not because of your description. Bones resist heat diffusion and meat doesn't come much bonier than necks.
Also consider how much work the neck does carrying that big head around. Those are well-developed muscles with a lot of supporting connective tissue.
If i were cooking it i would bone it, 4% brine the meat for up to 12 hours, dry, season if desired, and vacuum package as flat as possible.
If you are aiming for a traditional pulled pork result cook at 80C for 10 -12 hours. At that temperature heated water vapour will cause the bags to expand. To ensure even heating you will have to rig something to keep the bags submerged. I give the bags an occasional rotation to move the air bubble around during the cook because moist air insulates the neck meat.
If you expect a more conventional tender pork texture; brine, season, package and cook at 61C for 16 to 24 hours.