One of the temp sensors drives the dash gauge. The other informs the glow plug relay on the progress of the glow operation. They could have used one sensor, but they didn't, they never do.

.9-1.1 is the normal range of the glow plugs. The light in the dash will let you know if there's a problem. When it doesn't display a glow cycle, one of the plugs would have gone bad. Since your car was probably converted from series plugs, the relay may be non-stock. Leave it alone, you're going to find your share of problems without going out of your way to look for trouble.