xUmp offers a nice 4 ohm speaker similar construction to a 50 mm Fatboy. I use them in MTH engines if there is room, they sell for small money but not cheaply made.
Forum rules won’t let me post a link but they aren’t hard to find.
You could use a pair in series. I have used them in my Commodore Vanderbilt upgrade in this thread.
https://ogrforum.ogaugerr.com/...llmor-hudson-stage-1
Pete