I believe it's off an old Bullet but it might not be. It's made of cast iron. If anyone knows what this is I'd love to get some kind of an idea what it's for. The chamber ID is about 3.3"
On a slightly related note, the one thing I know for certain about this head is that it doesn't fit my bike, so if anyone wants it, it's available.
I have many more photos if another angle is needed for a positive ID.