Yes twin rudders with a skeg in between. (The narrow tapering stern made difficult access in my model. Eventually done by using a toothed belt to connect the rudders.)
Six torpedo tubes (She was very heavily armed) with doors.
John Lambert did not have drawings so I went to the Maritime Museum archive at Woolwich. Drawings cost me about £50 (then) for copying costs. I would love to be able to share them but copyright is a necessary evil!
Other useful sources are the RN submarine museum at Gosport. (Archive sources and very detailed photos for not too much money.) (BTW I will be at Gosport (with R4) on an AMS weekend at the RNSM 16/17th August)
Also look at a very interesting document BR3043 on this website:
BR 3043 has some drawings in it also as well as interesting specs etc.
Hope this helps. What type of model/ scale are you thinking about building?