SSRS / SSDT Custom Data Extension / Custom Query Designer

I have implemented a custom query designer for SSDT 2014 (Visual Studio 2013). I now need to move this over to SSDT 2017 (VS 2017.) Previously my custom C# assemblies were deployed to C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\PrivateAssemblies directory. This directory contained all the referenced assemblies which are:

Microsoft.ReportingServices.ProcessingObjectModel.dll
Microsoft.ReportingServices.QueryDesigners.dll
Microsoft.ReportingServices.Interfaces.dll

I get "An error occurred while loading the query designer" exception now when trying to launch the custom query designer.

Why does there not seem to be any guidance for creating a custom query designer extension? I believe this stuff was documented in SSRS 2008R2 and SSRS 2014. 

I have also found there seems to be 2 different version of these previously mentioned files. SSRS has them as v 14.0.xxx and SSDT (VS 2017) has 15.0.xxx

Please advise as to where files need deployed, and setting for the RSReportDesigner.config, RSPreviewPolicy.config, devenv.exe.config.

Thanks,

Larry