Carter Carb thermostatic valve assembly question

[bmillere24]

The engine in my '63 had been replace with a factory "crate" 289 at an unknown time.  At idle, when warm, the engine tends to run lean.  During a rebuild of the carburetor, we noticed the additional thermostatic valve added at the rear of the carb and attaches to a PCV.  My mechanic and I don't believe the second assembly is needed and the addition vacuum may be opening and adding extra air to the mixture.  Any thoughts on just capping this one outside of the carb off, or is it something needed?