A: Only if your Epic version was never updated beyond 2017. Most Epic installations started in 2020, so no. You would need to downgrade.
A: The mod likely uses a specific native function that was deprecated or changed after 877.1. You must use the exact game version or ask the mod author for a patch.
If you need this version, you likely already know why. Treat it with care: back up your files, scan for malware, and never, ever take it online. When installed correctly, it will unlock a library of classic mods that defined a generation of GTA V content creation.