Pete, that's about as much as I paid for the receiver I'm trying to improve!
A Radio Shack DX-394

Tom-

I missed your original posting. What does the DX-394 currently use as an IF
filter? If it happens to be made by Murata (or maybe Panasonic), a replacement
with better specifications may available to fit in the same PCB holes. Check
your filter's part number with the company's web site, and you may find a
solution there.

However, if it uses the same filter for AM reception, a tighter filter could
reduce sound quality of music.

73, Fred, K4DII