In reply to a visitor's (good catch!) request, i'm offering HERE a download link for Zurichess Basel for collectors. I couldn't test it under Marshmallow so i don't know whether this arm5 build works on Android versions beyond Kitkat.
Since Basel had been quickly replaced by Fribourg (mentioned in this old POST), i had not seen any interest in sharing it at that time. But frankly speaking, those were the times where the main intention was NOT to create a complete collection but rather to keep copies of the engines playing in Rapidroid.
Nowadays, the visitors seem to require all engines and all versions and even all different builds of the same versions, accessible in a unique repository. Well, okay, you're gonna get what you want!