Slant six heat riser

64Dart270 said
Yes, I understand it's function and relationship to proper choke operation

The heat riser has nothing to do with the choke on a slant-6. You're thinking of the V8 setup.

Since it does rotate with a little help from pliers, I should be able to free the rust

Chrysler P/N 4318039AC is the magic gookup to unstick heat risers. No idea what's in it, it's not just relabelled Liquid Wrench or anything similar. It works like nothing else.

where I might find a new spring?

Tough to find any more. You're going to be beating the NOS-parts vendor bushes.

choke spring is a bit oxidized as well and also tends to stick

Put in an Electric choke kit #1231.