Re: 97, 1500 GMC propane??
It's a bit dark so I cannot tell which system you have but yes, that is the vapor converter (the large vapor hose is a dead giveaway).
There are 3 different ways to deliver propane to the intake manifold -
1. Complex converter.
2. Simple converter
3. Vapor injection.
A complex system uses a single unit to convert the liquid propane into a vapor and then deliver it (via the large vapor tube) into the throat of the carb or intake manifold.
A simple system uses 2 units, one unit converts the liquid to vapor, the second unit delivers the vapor to the manifold.
As the propane is converted to vapor, it freezes into an ice block, heated water is required to stop this happening.
Propane injection requires a modified or custom manifold to house the injectors. There is also a CPU that iinterfaces with the vehicles ECM.
If you clean up the pic, I can identify what system you have although I'm pretty sure you have a simple.