Slant 6- Idle and Running

Yep, that heat riser shaft is definitely frozen.

People think WD 40 is a cure for everything but even though it smells good, it is not a rust penetrant. WD stands for Water Displacement and was the 40th formula tried.
For decades Mopar service manuals said to lubricate heat risers with their special lube. It is a secret formula penetrant/lubricant. I bought some on Amazon a couple years ago after SSD posted a link.