My guess is the coin is older. The 8R Mexican coin of 1755 has a diameter of 39 mm.
8R coins of the previous monarch (Felipe V) are of a diameter of 40 mm.
Based on my measurement, the coin of the IP is about 41.8 mm.
Though a real coin would not be that large (and I'm not suggesting the IP's coin is other that authentic), I would favor the older series 1732-47).
Don........