No apology required, I appreciate the interest, just wish I had more detailed info.
When I ordered the top ends from Terry he told me that the heads would not be cast until he had made changes to his existing patterns, which are an evolution of high performance Vincent heads he designed in the 1980s. He was in the midst of flow testing several new prototypes when I made the order. The best shape/design would be the type chosen for a batch of fourteen heads he planned to have made up, two of which were for my engine.
Terry has reconfigured the 1980s design several times over the years, then tested the results on his own bike both on dyno and on the salt. Around 2007 he sold smaller sized set of these heads (he has 84 & 92 Mm sizes) to the machinist/motorcycle racer Steve Hamel who wanted to revisit Rollie Free's Bomneville record of 1949. Steve wanted to see if he could break Rollie's record, but do it on pump gas rather than the alcohol fuel Rollie's Lightning ran. Steve revamped Terry's high performance heads considerably and upped the output of his 998cc machine to over 100rwhp then with further mods 120 rwhp. Here is his bike at the 100 HP stage. https://m.youtube.com/?#/watch?v=z6SpCobouDc
He did break Rollie's record with that bike.
This made Terry take notice, so he incorporated some but not all of Steve's modifications in another new design, the one he was busy flow testing when I made my order in early 2010. I received the heads in early 2011. Terry did not incorporate all of Steve's changes as Steve's is a/Bonneville racer, top end only type engine and Terry wanted to keep a strong level of midrange power with his design. I can attest to the fact that he got that right.
So all of the R&D has been done by Terry Prince and Steve Hamel , some of it going back to the 70s. That's what make these top ends relatively good value, it's not so much the foundry work and machining which goes into a current set as it is all of the expensive R&D that went on to get here., much of it trial and error I'm sure.