Hello! Both Three and Babylon shaders are written in the same language, GLSL, so it should be fairly straightforward. Having a quick look at it, the most involved part seems to be the BVH structure, as you’d have to port that to Babylon too.
The uniforms are different from engine to engine. They might have the same name for time to time, but in general they are not the same. This is the list of built in uniforms: