This shows the side of the port and how the runner blends, as viewed through the valve seat.

I could mail the HammerHead to you so that we could learn a few things.  You could run it up on your flow bench so we could compare data between the two benches, and you could do a thorough dimensional comparison.  If it is not too crazy expensive, I would be willing to pay postage to you if you are willing to pay the return postage.  I want to use the HammerHead for my Stage 4 head project, so I need it back.  But you are welcome to use it in the interim.  I think it would be a good collaboration.

If you are willing to share your city and country, I can check with our postal service to see what it might cost to send it.

Finn, I just thought of something else.  You are testing at a very high differential.  The air velocity is also very high.  Your clay may be shifting.

When I first started messing with the port flow, I had trouble keeping the clay in the dipsy-doodle.   The tests results were inconsistent, and I ultimately gave up on the clay because it kept pulling out of the dipsy-doodle.  I was doing the tests on the HammerHead, and since that is my test mule and will never be installed on an operational engine, I went ahead and filled in the dipsy-doodle with epoxy.  The intent was to determine if there was anything to be gained by filling it in.

If I could shift the clay with my anemic setup, you certainly could shift the clay with your supercharged bench.  You might wanna consider lowering your test pressure just to find the sweet spots for the filler material.  Then, once you have determined the correct geometry, replicate the shape with epoxy and test at 28".

If you don't get it just right, it's easy to make adjustments, add filler, or remove the epoxy and do it over.

After smoothing the cuts a bit, I start to bend the cone in the vice:

After a trip to the lathe, some welding, it ends up on the front of the muffler

That is a sweet lookin exhaust system.  How did you attach the mount to the muffler?  Do you have any pics.  I've been contemplating stainless steel pop rivets.

Can't wait to see how you construct the baffle.

This 50mmØ clamp piece is to be joined to the internal 45mmØ baffle tube, so it has to be swaged into a smaller diameter at the one end. This is done by chucking it around a brass mandrel (steel would do as well, brass was what I had on hand in the right dimension) with a couple millimeters overhang, then just hit it with a hammer and lay the edge down on the mandrel, This is surprisingly easy to do. (well surprising to me since it is the first time I tried to do a thing like that.)