I have big blocks, small blocks, twin turbo small block, LS supercharged etc. I been there done that. Go with a LS based engine. Better design all around and will be much easier to sell in the future. Kurt Urban did my twin turbo smallblock in the Mule. I would recommend Kurt or Brian Thomson
http://www.thomsonautomotive.com/?page=about.cfm
Brian is who built Stielow's engine in the red Devil and can build a LS engine to suit you. He knows what it takes to make them hold up. He and Kurt will both give you real dyno #'s not just made up magazine #'s