That is the procedere:
You need a spare track of your analogue tape machine onto which you record a rythmical signal, e.g. a MIDI metronome, I call it the "sync track".
You record a track on the left channel of your soundcard and the sync track to the right channel, so you end up with as many stereo files as your analogue tape machine has tracks minus one.
Now you can sync the tracks. If your tape machine has an even transport with low drift, it should be easy. If not:
Get a cute program which can alter pitch and tempo of a wave file, possibly even automatically according to a rythm. "Beat detection", "tempo change", "resampling". So you can normalize all tracks to one tempo sheet.