If you choose the correct service kit for your Air Top 2000 heater, then it will come correct to suit the sensor/glowpin etc. It's very important that the service kit matches your heater type.
If you have a 2000S then purchase a 2000S service kit
If you have a 2000ST or STC then purchase a 2000ST or 2000STC service kit
You should NOT ever have to drill new holes ....