I used to have Audacity on XP, I'll look.

Gold Wave is what I use to mess with conversions. It is also an excellent little wave editor and recorder. It's free to try and only something like $50 for lifetime updates. 
https://www.goldwave.com/
 
Did you know you can drag and drop audio from a project. 
 
And to export 2 tracks as a stereo file simply just pan then hard left and right. Solo them and then export to WAVE. Then use Gold Wave to convert to MP3 and put in drop box. Make sure the MP3 format is set to preserve stereo image. Gold wave has all the different mp3 formats to choose from..I'd use 320. 
 
If your project has a tempo then let your freind know what it is. OR
If there is any midi at all you can easily "save as" a MID. file and all the midi tracks will be saved together with the tempo. Midi files are super small. Your friend can open the MIDI file in PT then drop the audio tracks in and all should sync up pretty good. I've done this with a freind who uses Garage Band. 

mps3 have a slight offset with them, so can vary slightly even if created from a broadcast wav. mp3 is a good format for sharing if the wav material is already available at each DAW being used. In your situation, using a single percussive hit on a blank section at both beginning/end of the song gives a "quick and dirty" alignment guide for both of you (mate the first and check that the second matches). Then you just lop both ends off after mixing is done.
 
I typically will bounce the desired tracks to a new track first, then convert that to an mp3 externally just to verify each step.

That's a good point about MP3 timing, I actually leave everything as WAV. and have been lucky that my collaborators live in the same town so I hand deliver. 
 
I've used the transient spike trick a few times. It works.