Highest flowing sbm heads?

The W5’s use W2 rocker gear, the milled stands for the rockers are the obstacle here. TD or Jesel rockers. Maybe Crower as well. I’m not sure about that.

Then porting and valves.

Locks, retainers and springs will work with the cam intended and the valve stem height. For me, this is not part of the head cost since it works with the cam. It’s part of the cam and valve train cost separate from the head for the most part. Setting them up is easy IMO. If your paying the man to put them on the head, then that’s on you and the added cost of laying the man is added.