Can you post a pic of the Mugen v's standard head? Air cooled is not easy.Big question is cast or machined, cast would be a better option but adds some issues. Machined from solid has a different set of hurdles.You will quickly become bored with this.
Casting.
A wooden or MDF copy of the head would have to be made then the casting made from that.If you wanted a 1 off a foam or wax head could be made, then the item made from those but the mould is destroyed when the molten ali is poured.Then there is the final machining of the casting. Cost for 1 off astronomical and depending on the casting tooling cheaper the more you churn out.
Machined
First is material, how ever much the big bit of billet costs 75% of the material will end up as swarf. Next is it can only be made as well as it's been drawn up. Good news is when machining is finished the job is finished.Manual machining will cost a large fortune and CNC cost a small fortune.Again the more made the cheaper the unit cost.
If you go through with it will appreciate the quality of Honda OEM castings.
Why would you make a DG head when spinning a standard head on the lathe can yield better results