Maybe this will help someone else with issues installing Houdini Engine on source in Unreal–I had to change the path in HoudiniEngine.build.cs file on lines 90 and 122 to the drive and path where I installed Houdini. I don’t have it on my C:. I also changed the path name from \Side Effects Software to \SideFX. Unsure if it also helped but I updated the version string to 19.5.303. Build succeeded and Houdini Engine is in editor.