I could help narrow down knobs if you can find the manufacturer of the heater. It does not appear to be a Harrison/GM product. That being said there were numerous other manufacturers in the 30’s - 50’s that built heaters. These vintage heaters usually had Bakelite or plastic knobs which is why they may have been replaced, they deteriorate over time. Chevs of the 40’s has replacement knobs like these, which would be period correct.
https://www.flickr.com/photos/advance-design_parts_co/9201965046/in/album-72157631868452754/
The vent you reference again I could narrow down if you know the manufacturer of the heater. Harrison used simple levers in many cases for the defroster settings.
https://www.flickr.com/photos/advance-design_parts_co/8129330842/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/15591819373/in/album-72157631868452754/
There are many varied styles in knobs and applications.
https://www.flickr.com/photos/advance-design_parts_co/25214888437/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/43790194650/in/album-72157631868452754/
It will be easier to find GM or Ford reproduction knobs as they are the predominant survivors.

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr