Here is a link to a Hydroflame Furnace dealer. Apparently they are still made and are available:
(Has Atwood and Traco - seems both use the name Hydro Flame.)
Hmm. What is the large round thing? All the pictures on the website show a rectangular shoe box type shape.
Looking at your photo again, the tube in front of the white dial seems to be pinched.
In your picture, it doesn't look like the round door is closed by the thumb nut. Rotate the door open, unscrew the nut, close the door and screw the nut tight closing the door tightly.
There is that cigar shaped object. Looks like some kind of pick up for heat control. Is that supposed to go into the round burner?
Here is a Hydroflame troubleshooting website:
I presume we are looking at the furnace through an outside access door?
Another point, after 37 years, who knows what modifications a previous owner did.
All the websites reccommend utilizing a certified gas mechanic. Probably a good idea. Gas is dangerous.
Good Luck and Happy New Year.