> Folks have indicated tempo changes are needed while others have said they are not! But no one could fully answer his question. Until now!

No, it is trivial to line up 4/4 and 12/8. Tempo changes are not required.
A tempo 80 piece in 4/4 will line perfectly with a tempo 80 piece in 12/8 (compound time signature)
A song at a tempo of 80 is the same exactly whether it is 4/4 or 12/8.
Bach;s Jesu Joy of man’s desiring is the same tempo in 3/4 of or 9/8. In fact I posted a score of it higher in this thread where both time signatures are used interchangeably.for different voices of the same chart,

The people who say differently haven’t correctly set their DAW to 12/8 (compound time signature), and have mistakenly set it to two 8th notes per beat instead of 3. So they get a wacky tempo for the 12/8 because they aren’t in 12/8 triplet (compound).

Dan. My advice to you, is to render the files to audio, then you can make sure they don’t get messed with when you drag them from program to program. You will find that 32 bars of 4/4 at tempo 60 is a wave file of 128 seconds. And 32 bars of 12/8 at same tempo of 60 is a WAV file of 128 seconds. And then you need to ask yourself if you’re going to be able to line up two WAV files , both of 128 seconds.

Have Fun!
Peter Gannon
PG Music Inc.