One additional twist, the auto tensioner doesn't seem to be the correct one. There is no 17mm boss or any other attachment point for levering the tensioner in a counter-clockwise direction. I managed a workaround, but it was a giant pain. The slightly larger pulley size wasn't an issue, probably because of some belt stretch. The belt is not in as good a condition as I had hoped, so I'll order a Gates replacement.
I took it out for a quick test drive and gradually worked up to some strong pulls. Seems like I'm up and running again. I did note that at wide open throttle, the tune was clearly going to let me get into redline territory. Maybe that's a bug of that particular tune. This car is mainly for commuting, so it shouldn't be an issue if stay alert.