I use the (also free) Paint.Net. Basic flow:
Crop and size down to say 800x880.
Open the Obverse, resize the canvas to 800h 1600w
Copy the reverse 800x800 image and paste as new layer
Move the selection to the right margin
Merge down.
-----Burton
50+ year / Life / Emeritus
ANA member (joined 12/1/1973)
Life member: Numismatics International, CONECA
Member: TNA, FtWCC, NETCC, EveryCountry (online) coin club
Owned by three cats and a wife of 40+ years (joined 1983)
Author: 3rd Edition of the Sample Slabs book,
https://www.sampleslabs.info/