I'm not completely familiar with rallisprint rules, but those number signs seem to represent some segments of the stage. Rallisprint is a form of motorsport where you create a track out of roads and you can drive also on rallycross cars because the way back to to the service and start of the stage doesn't involve driving on open public roads. Everyone drives two passes, with no pace notes.
Here's pictures from the event, you can see that car #10 is a Corvette :D https://www.rallikuvat.net/2005/kankaanpaa/
Kankaanpää, quite far from Rally Finland.
The video looks awesome, but the biggest reason for that is the old incar camera. If that was a modern GoPro with a wide angle lense showing out from both side windows, it would look bland...
Here's another old RWD incar which looks totally crazy thanks to the camera angle and lense. This is a part of the Juupajoki stage driven often in Rally Finland https://www.youtube.com/watch?v=R2ywOOOc-sc

