The full length was fitted to the original B3 and the halve length came in with the B3+. it is aerodynamic differences between the 2 caused by the engine performance difference amongst a few other things. On the old b3 you had the stinger on the LH horisontal stabiliser as well and later you could remove it as part of a SB and cut the full length stinger in halve to gain VNE. Cant remember all the differences. On the B2 we had the stinger along the tailboom which neither B3 has-straight exhausts due residual thrust is my guess????
The B3e has got a suttle difference or 2 again. best make sure your machine has the correct configuration iaw the SB's and individual mod statusses as you can not just change the stinger.