Code versioning software, e.g. Perforce, GitHub, includes code manipulation features, e.g. compare, merge, in addition to journalized source code storage.
May I suggest that you also consider encouraging the use of my ARM code management software. If it doesn't already work with APL64 then it should be able to with trivial changes (such as checking for a new ⎕SYSID).
ARM is tightly integrated into the APL interactive session philosophy and does not require import/export of code to external files, nor external command processing of those files with a commercial code-versioning system. It is used directly from the workspace, reading and writing APL objects natively, using no software besides APL itself. It provides virtually all the features needed for APL that the traditional software management packages provide, and does it in a much easier and faster way than having to coerce APL into working in the way for which they were designed.
I would like to confirm certain kinds of support that APL64 provides so that I can make sure it with work well with ARM, and will provide it free of charge for use with both old and new styles of APL.