Every time this issue pops up I make a mental note to post about the Whiteline rear stb. I do and then everyone ignores it. Well, here goes again....
WHITELINE in Australia makes front and rear STBs for N14 Pulsars. Since the mechanical parts and dimensions of the chassis undercarriage are identical between N14s and B13s, anything for the N14 should fit right in on a B13.
Those guys have a rear STB for N14s, they sell it rather cheaply ther (~US$70) and they are represented by at least 3 companies in the States.
Go to
http://www.whiteline.com.au
and search for US distributors. Then, go buy yourselves a rear STB.
Chris