Hi so basically that is exactly what I intend to do. The customer pays 270 GBP then when the coin is finished they will send 1 BTC so I will then ship the coin and then fund when the coin arrives to the purchaser. This way there is absolutely zero risk of the volatility of the bitcoin value.
That still doesn't solve the pre-order arrangement, I think that is also a concern. Do you have firm quotes for your fabrication/machining costs? What about variations in the price of silver?