Apart from the 3D model, I don't know much about the rest, textures, UVs etc. As I said, I don't make renders.
Anyway, there is a very simple method to transfer 8.1 models to 8: load them both to Daz and try to fit the aspect ratio of 8.1 to 8 as precisely as possible, send them to Zbrush and select 8.1, go back to Daz, delete 8.1, go back to Zbrush again and send 8.1 back to Daz. The usual Goz dialog box will pop up, and choose to set the 8.1 morph to 8. Everything works fine.