Thanks to the above for the help!

I posted some new pictures; it's been pretty cloudy outside but it cleared up a bit today.

As you can see, there is no maker's mark on the receiver. There's actually not a single Japaneseicon character on the entire rifle. The only thing I could find was the two-digit number "60". Arggh! I wish I had asked the seller where he had gotten it!

Hope that helps!