Yeah with the increased need for oiling on the exhaust side I would be careful with using a positive type seal on the exhaust side. I have worked with a twin turbo project on my chevy v-8 powered jag, and as long as the valve guides are good, there will only be back pressure on the exhaust valves with the turbo in place especially. I would recommend going with the facoty exhaust seals on the exhaust side, they are probably designed to allow for a little bit of oiling on the stems which will keep the stems cooler, straighter and less worn.