You are correct. I have had conversations with speedmaster about buying bare castings by the pallet, to do in house. Same thing those other guys do. But as a one man shop, just couldn't justify building 30 sets at a time, to sell a pair on occasion
When I called and talked to the owner of ProMax he said I wouldn’t believe how raw those heads were when they arrived. But that’s how they wanted them. I’m sure most vendors get them from Speedmaster in a semi finished condition like we do. Then they port and do a valve job like I do. Where ProMax wants to install seats, guides, cnc if ordered that way, and a valve job. All in house American jobs.