Try using a 100w light bulb with the probe against it and wrap it with some fiberglass insulation that should get plenty hot. Any fluctuations from this range can damage the engine.

Us 16 62 30 Off Digital Infrared Thermometer Non Contact Laser Ir Temperature Lcd Display Gun Pyrometer Tester Aquarium Temperature
How to test a pyrometer gauge. The short version is this. Check gauge resistance 1. Attach the temperature sensor probe to the gauge. On a work bench away from the vehicle connect the gauge up to a 12 volt source 2. Check wires on studs to make sure wire colors match labels on studs. Do the same with some ice.
A pyrometer measures the temperature of the engine through its exhaust fumes. If the pyrometer is slow or erratic check the leadwires and thermocouple for continuity and check the leadwires for resistance 023 ohms per foot. Found an isspro installation sheet in the box with a new gauge my father has. The tool can then be adjusted to reflect the accurate measurement provided by the thermocouple. Should give you a high low calibration. A somewhat accurate method of calibration with a thermocouple involves simply measuring the temperature of an object with a trusted thermocouple then measuring it with the pyrometer.
With power off disconnect the four wire connector from wire harness that goes to amplifier box 2. With a bbq gas lighter heat the probe end being careful not to burn yourself. A probe is placed within the flow of exhaust air to receive the best gauge of how hot the engine fumes are becoming. Within a minute the gauge should rise and the temperature on the gauge. Normal operating ranges are from 300 degrees to 1200 degrees. Bring some water to boil and check the temp with another therm and then check the temp with your pyro.
If you have a heat source with a known temperature you could test the probe and hook up a millivolt meter to see if its the probe or gauge. If you want to blow the pictures up it may be usefull sometime.