$40,000.00 to make these gear sets. He is not rich and is not a big Co that make anything larger. This is ther smallest run they will make. These gear sets will only work in R230 rear ends. They will only fit Z32's and Infinity Q45's. They will not fit anything else you mentioned.
Call up burns Stainless tomorrow and ask them how much it costs for enough Inconel tube two make just 2 three Cyl manifolds. The price will be over $2500.00 for just the tube without welding anything or making flanges. Running a short manifold on a high boost turb car will crack in anything but stainless. In order to keep everything bolting up normal for a true bolt on in a car with such a tight area it needs to be this way.