2022.07.27 Reprojection Math in UE5

I'm very close to getting Reprojection working in Unreal but something is wrong... probably has something to do with the fact that I'm having to deconstruct and reconstruct Matrix4x4s with custom code when I pass it from Blueprints to the Material (shader), because for some reason it's not supported. šŸ˜¤

Blueprint for getting Camera's ViewProjection Matrix and sending it to the Material

Material nodes for taking vertex (I hope) world position, multiplying it by camera's view projection matrix, and sampling RenderTarget texture (output from source camera)

Custom expression HLSL code for Custom node in the pic to the left

For some reason this material applied to a cube results in a strangely rotated and stretched representation of the source camera's RenderTarget texture...