Roy,
I've searched the documentation that I have here and finally ended up on Google. Here's an ad that I found:
Looking for filters for a heath 301 receiver . The filter numbers are AM-
404-314 AND THE CW- is 404-284. please get back if you have one or both.
thanks
That would leave only one possibility, the SSB filter. That is backed up by a picture that shows the 404-200 mounted in the middle position.
I hope that helps a bit,
I have a couple of SB-303's here. One is loaded with filters, including the AM filter. It's as you say, not a great one but not bad either. It sure won't give you hi-fi but it can sort out the crap pretty nicely. There are several very serious attempts to make or modify one of the standard filters to make a 6 khz one. I have doc here somewhere that gives the details on how to do it. That would put it in the right category, and then teamed up with a nice little DX60 and an SB220 .. whew .. what a nice setup that would be!
--Larry W8ER