Chris,

Just to stick my oar in here - here in New Zealand it also doesn't count as
a twin. Even our logbooks state you can't log time as multi if it's
centre-line thrust.

Interesting. In the early '60s when Cessna certified the 336, it
asked the FAA to allow single-engine pilots to fly it; FAA said no,
have to have a multi-engine rating. Also, those military pilots who
flew the F-4 Phantom and then obtained U.S. civilian ratings based on
military experience were given centerline thrust limitations on their
ratings, apparently due to the close proximity of the engines and the
relatively mild yaw on loss of one.

All the best,
Rick