I recently installed a new, more powerfull engine in my RS4 racer 2. While doing some testing at the local track, one of the motor mounts came loose, and it backed out just enough to eat up 4-5 teeth on the gear. It was a 44 tooth, and the only thing my LHS had was a 43 tooth. Can I use the the 43 even though it's not listed in the chart? I understand it's supposed to create issues, but will one tooth make that big of a difference?

yes, it won't mesh properly...the combination of 1st gear clutchbell and spur teeth has to add up to the same number of 2nd gear clutchbell and spur teeth or you will not be able to have both first and second gear sets touching at the same time

I see, oh well, I guess I'll just reinstall the single speed for the races on Sunday, and wait for the gear I need to arrive...