Hgguru but the older versions aren't available to download
Spine allows you to run any older version found on the changelog page back to 2.1.27.
You need Spine to do exports. You can import the JSON files into 3.8 and then export them using the UI. I don't remember if 3.8 can take JSON as input on the CLI to do exports.
You can import your JSON into Spine and save a .spine
project file, then you can export the project file with any newer version of Spine. The latest version has the most features, currently 4.2. I don't remember if 3.8 has a CLI option to import a JSON file and save a .spine
file. If not, you'll have to use the UI to do that step.