I have no information spicific to your heater but the sensor might be a thermocouple. Look at one in any hardware/plumbing store to see if that's what it is. There would be a button or leaver on the control valve similar to that found on some water heaters. If it is a thermocouple,it is mounted so the pilot flame touches the tip.

I am figuring it is a thermocouple, though the shape of it is different, it is the shape of a pen, and the control valve on the heater is exactly like a water heater valve. The only information I have ever been able to find on it is by searching the patent number. It turns out this heater is the original ventless shop heater, made around 1972.

Sounds like a sensing bulb for a thermostatic control to me. I would think there should be either holes below or behind the burner area to mount it.

This may be a part of the Oxygen Depletion System (ODS). It being the first ventless made it may not have had a very reliable or robust ods. Your first move prior to firing this in an enclosed space is to get a GOOD CO detector. The pilot assembly on vent free heaters are built as a non adjustable assembly. They are very very carefully calibrated to provide reliable operation and safety. Many of the components of this assembly are specific to that manuf and likely are not off the shelf components. Good luck getting it going, but be real careful.

It turns out after searching around, it is the remote hydraulic sensor bulb. I just need to figure out where to place it and how to mount it.

As for CO problems, I do keep a CO detector in the shop, plus it is not very well sealed, so carbon monoxide is not a problem, besides I have a wood burning stove in there that also helps ventilate.

The assembly on it is used in a large number of shop heaters, even to this day is still available for purchase.