I for my part prefer using my German PS in this way (I try to translate the commands):
Use same height for both images.
Open the first image in PS.
Use Bild >>> Arbeitsfläche (Image >>> worktop?) see screenshot:
give it the new with, by clicking into the left or the right indicating hand by playing around (try and error) .
Now you can insert your second image and use it as a single image.
Select two images,
Go to Print module
Choose- Single Image/Contact Sheet
Set: Rows=1 Columns=2, adjust margins etc,
Click button [Print to File]
Akash Sharma's (before, its deleted now, why whatever) and wobertc's hints are fine in my eyes, BUT I for my part don't like to be without being a party to the proceedings! (Oh sorry in German language it would be a simple "Ich mag es nicht "Herr des Verfahrens" zu sein!")
With Lightroom you can be the 'Lord' of design!
The "Single Image/Contact Sheet" is simple, neat, adjustable (Cell padding, etc).
The "Custom Package" in Print Module makes the OPs task even easier- Freehand designing!
many thanks for your effective solution. I didn't use LR over a longer period of time, but this could be a reason to load it down and deal with it in detail, esp. to try out your suggestions for myself.
I wish you (all here) with your families a merry christmas, joyful holidays and of course a good start in a happy, successful new year.