Yep, it's interesting how the inline makes it look so much smaller. In reality the Swordfish was only longer by one
additional fuselage bay, 2', and the wingspan was only 6" greater. The enlarged fin of the Swordfish is what creates
the visual difference.
A single-stage Merlin would fit easily as its not much different in terms of external dimensions when compared to
the supercharged Kestrel IIMS used on the S.9/30. A Hurricane I or, better yet, a Battle or Fulmar nose would
probably fit fairly well.
The 9-cylinder R-1820 along with the Hercules, R-1830 and Gnome-Rhone 14-cylinder engines are all viable re-engining
possibilities. Heck, why not a Nakajima Sakae on an IJN variant? Single row engines like the R-1820 could have the
standard short-chord or full NACA-type cowlings, see the Blackburn Shark for applicable real world examples.
... and as a blast-from-the-past three of Jennings Heilig's Stringbag What-Ifs:
899 Swordfish
Coral Sea Swordfish
Faireishi
From Madoc Pope's kindly hosted archive page:
http://www.madoc.us/profiles.html