B3/S124:
  o.o
  ..o
  ..o
  o.o  (c/2)
B34/S356:
  .o..o
  ooo.o
  .o..o  (c/4)
B35/S134:
  ..o.  (Cute! One more cell and it'd be a Life lightweight; one less 
  ...o  and it'd be a Life glider; instead it's a c/3, and the other 
  oooo  two generations look nothing like a lightweight or a glider.)
  oo..
  ...o
  ...o
  oo..  (c/6)
So far, aside from some haphazard looking, I've searched for
spaceships one of whose generations will fit in a 3x4 rectangle in the
following rules:
  B2/Snnnn   where nnnn is all combinations up to 0123
  B3/Snnnn   where nnnn is all combinations up to 0123 as well as
             4, 04, 14, 014, 24, 024, 124, 0124.
Aside from the one ship in B3/S124 shown above, the only spaceships of
this size (with period up to 20) in any of these rules are the Life
glider and the three known from B2/ (each of which also is found in
some variants of the Life or B2/ rules).
-- 
- Rich Holmes
                Of course it's daft, it's traditional.
                                            - Terry Pratchett
>So far, aside from some haphazard looking, I've searched for
>spaceships one of whose generations will fit in a 3x4 rectangle in the
>following rules:
>
>  B2/Snnnn   where nnnn is all combinations up to 0123
>  B3/Snnnn   where nnnn is all combinations up to 0123 as well as
>	     4, 04, 14, 014, 24, 024, 124, 0124.
I misspoke; I hadn't yet done B3/S0124.  That turns out to have one
small spaceship, moving diagonally up and left at c/14 with period 14
(glide reflection at generation 7):
  .OO
  ...
  O..
  O..
This also is the only spaceship for this rule in a larger area, 4x5.
I've now done some more searching and found two more spaceships, both
in B3/S35:
  .OO       OOO.
  .OO  and  ..OO
  OOO       OOO.
  O..
Both are orthogonal to the right.  The first of these has speed c/2
and period 8, with a rather interesting history: generation 2 looks
like gen. 0 with an extra, trailing bit; then gen. 4 is a glide
reflection of gen. 2, etc.  Random initial fields with this rule tend
to evolve to a rather sparse state, but I've seen this spaceship
produced from a random initial state that was sufficiently large.
The second has speed c/2, period 2.  This one also works in B3/S035;
the first is no longer a spaceship but a minimalist puffer train,
leaving behind a trail of isolated cells!