I am not 100% on your 79, but have been told that one should have the same B2B as ny 81. Your pic wa a little dark, seems to appear different than the B2B in my 81.
Have some photos of the B2B but I cannot get this foul new program to cooperate. After removing the circlip and the round cover your should be able to pull it right out. It is the large round cover on the rt rear of the trans. Has a smooth round metal cover, B2B is under that. Biggest round cover on the tranny.