Problem with Append

Hi all.

I have a problem with the Append function.

I want to merge two project files with different bpm values.
The first has 90 bpm, and the second has 120 bpm.
The second file is the second part of the piece; but I accidentally wrote it with a different tempo.

After appending them together, I time shifted the second part of the piece so it plays directly after the first part.
Unfortunately the tempo of the second project has been reduced by the Append operation to match 90 bpm: so the whole thing sounds much too slow.

Is there a simple way to merge these projects whilst maintaining the correct tempo in both?