Yes, stators can test good and still be bad. I only get rewound stators from Kev. Always good. Not worth the head aches. The only other thing I could not see in this thread, (might of missed it) is you haven't check the pick up coil to see if the ohms are correct. They can reek havoc. The 600's have a different ohm than the big blocks. I had a 600 once that was off a few ohms and would not spark under compression only when pulled out of cylinder. Check your ohms on that before going any further.If I read you correctly the week spark moved from the dual coil to the single coil (2 to 3). Just to verify, you unscrewed each wire from the coil and moved it one place to the right? Some models you can unscrew the wire from the coil and others you cannot. If this is the case, to me, this would indicate everything up to and including your coils are good and the issue is from the wire out to the plug.
You mentioned that the spark was bright the first two hits and then fades. This is just the case for the one week wire, correct?
If it were me I would build up some new wires with new caps.
If anyone else following along has another perspective I encourage them to chime in.
I generally find comments like "all aftermarket stators are junk" to not be very useful. Stators are not complex items and any competent rewind facility should have no trouble delivering an adequate product.