Indeed, it’s +X Forward and +Z Up in Unreal Engine. I’ve exported with those settings instead of the original (Blender) axises, still the same. The solid white issue also came up at one point, but I managed to fix it. Also, where I live, WinRAR has an infinite trial period (no joke), so you can use that to zip/unzip.
I haven’t contacted JSM, because he has long since stopped working on the project those models were meant for.