It's a Rock Solid Engines billet head. Australian made. They built the engine. They order castings and machine them locally. It's pretty worked: port, polish, timing altered, billet bits etc. about 4.5hp. They also offer a 7hp motor, which is about max that a HT can handle with some reliability. I'm planning on adding a few more hot up parts soon.
The tank ended up costing quite a bit in stainless steel, but was worth it. I actually mounted the stock peanut tank to get it going but cracked the tank where the stud goes by over tightening it. The tank was still loose when it cracked! The imported stuff leaves a little to be desired...