Do you give a true internal and sincere ascent to it?
No, I am required to give true and internal assent to it.
By it I mean any act of the authentic Magisterium (from which I exclude SH).
But, in principle, indeed, Catholics must give true and internal assent to such acts of the authentic Magisterium.
Your problem is in misdefining what this "assent" entails. It's RELIGIOUS assent. Please read your hero Msgr. Fenton on the authority of Encyclicals wherein he clearly defines all these concepts.