I spoke to Harrop the other day & yes they do do a HTV1900 to LS1 T/B adapter in straight but yeh they still haven't sent me the pics.
They also mentioned a company, Auto Techniques 03 97631195, is in the process of developing a twin T/B that will be a direct bolt on on the HTV1900, so i rang them spoke to Scott, he suggested they will be ready in about 3 weeks, he couldn't give me any other info at this stage.