I have a set of Nicson Aluminum water cooled exhaust manifolds for marine use. These were on a 215 and will fit the 300/340 as well. One is cracked, see pic. These must be very hard to find, I found no information on the internet about Buick versions of these. I also have a splined drive adapter that bolts to the flywheel and drive's the out board unit. $100 obo plus shipping. Thanks Brent
