You really don't need a thermo. Wrap it in Butcher paper at the 4 hr mark and cook it to probe tender another hr to hr&half normally. The point is going to get done sooner than the flat concentrate on the flat either in temp or probing yo get the flat right the point will take care of it's self.
I never met a Cow that I didn't like with a little Salt & Pepper! Certified PORK-A-HOLIC