It is a marine picco p-21 this case is only used on the marine version, I think they called it a SE (side Exhaust) would need to see the other side. The car and airplane version share a case. but all the internal parts are the same.
do you have the machined stub so the header can mount on it with silicon as per like other marine engines it screws to the case first then the header with the silcon on to the stub.