John –
The NEC 3D works fine on the Amiga; I'm using one now. You _do_ need a
special cable, though. Redmond cable is where I got mine, and it's operated
flawlessly.
I don't think the Seiko CM1440 will work. If I remember the specs, it
doesn't have a wide enough horizontal sync range. Some specs I've seen in
reviews lead me to believe it only has two sync rates, but I could very
well be wrong about that.
Hope this helps some.
Harry