Real Model of the Czech Republic makes a 1/35 Detroit Diesel 8V92TA for the Hobby Boss HET that might work. It's a full engine & transmission, and is €28 ($39). So it's about double the price of the kit.
http://realmodel.cz/index.php?page=shop.product_details&flypage=garden_flypage.tpl&product_id=477&category_id=19&option=com_virtuemart&Itemid=79