Counterfeit 1775 Halfpenny - Machin Mills?

I agree with you, the date does appear to be 1775, but in my opinion, this does not appear to be a Machin's Mills issue. There is a website that I use that has die pair charts of the different varieties of Machin's Mills halfpence. It can be found here: http://exonumismatics.com/survey/survey.html. If you scroll down to part C, they have a nice write-up of the different types and have links to four die pair charts.

It was not uncommon at the time for this particular issue to be counterfeited, and I read somewhere that by the time these pieces would have circulated, about half of the copper coins in circulation in Britain were fakes. Most of those were underweight and had poor quality designs. I find the varieties of those designs to be quite interesting, as they vary greatly from piece to piece.

The way I understand it, this was part of the reason that the cartwheel penny and two-pence were issued in 1797. Due to the rampant counterfeiting, George III wanted the public to place its trust in the currency again, and the standard was changed so that an ounce of copper was worth a penny. Thus, the one-ounce cartwheel penny and two-ounce cartwheel two-pence were created.