It is not an easy task, as 2.1.27 is more than 4 years old with hundreds of Spine releases since then. Also, the way scale is calculated has changed since 2.1.27, so if you use scale you will likely have to fix it up once you get your data into 2.1.27. It is likely easier to update to the latest runtimes.
You could do an export using 2.1.27 and compare the JSON to what you export from the latest Spine, then use a text editor to modify your latest export to match the 2.1.27 format.