If these tracks were recorded by reaper then the sources should have been recorded as Broadcast Wave Format (BWF) files. This means that REAPER should be able to time align them to the sample for you. Then all you have to worry about is matching the levels until the unwanted bit nulls.
Remember to invert the phase on only one of the tracks.
TO time align both tracks, select them both and then right-click/Item processing/Move items to source preferred position.
With faders further apart than the null point, the result will become louder; closer to null, quieter; at null, cancelled.
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