Given that I need a calculator to add two low numbers... someone else might want to check this over, but Donnie has an 89-point lead going to Kawartha.
If Thomson didn't qualify in the top five and didn't lead a lap (i.e. no bonus points)... and if Gibbons won the race (162 pts.), earned the pole (5 pts.), led a lap (4 pts.) and led the most laps (4 pts.) for a 175-point event....
Donnie would only have to start the race and finish better than 32nd (and thereby collect 88 points) or better to clinch Nat'l championship #5.
If only 32 cars show up, he clinches it at the green, according to my math (if Gibbons wins the pole and Donnie starts 6th or worse).