Chinese Fat Man Fake?

Unfortunately I suspect you are right. The final picture showing the edge - shows what appears to be split top reeds and evidence of edge grinding. That is typical of a copy that is edged in a ring die.

I could be wrong (it is only a picture) but you should check S.G before doing a more destructive acid test.

The finish on the surface looks like a cast, as well. The writing looks correct. The details, around the edges on reverse and obverse, look fake- very weak in places. Could it be a silver wash on lead, as a guess? Have you tried ringing it- putting it down on a wood surface so you can hear the ring of silver, or the clunk of base metal- This is an old test for counterfeits- counting houses and bankers hired people whose only task was to ring the money that was passing through the shop.