I have a set of 6" over polished stainless imco risers for mercruiser manifolds. They wouldn't fit under my rear fishing deck so I had to procure a set of 3" overseas. They were mated to glm aluminium manifolds. They have drains as I run closed cooling and always flushed and drained them after use. I paid over $1200 for them and would let them go for $600 + the ride.