JW - I had the same problemo.  I looked thru the parts pages and the #3 or #5 (whichever is used on the B) mower pitman parts looked pretty much the same as the #4 parts.  If I remember right, the #3 and #5 even use the same pitman parts, it might be the stick is different length.  Anyway I called our local (4 hours away) AGCO dealer and he agreed that it looked like the parts were the same.  I ordered the sickle end parts - clamp, frame, spring, as well as the tool.  They worked fine on my #4, they looked exactly the same as the old parts  (except not broke or worn out).  This year the other end of the pitman wore out, but I was lucky enough to stumble onto a #4 mower at an auction and I picked it up pretty reasonably and scavenged the parts.  I think Jim at OK parts told me once he had a few B mowers he would part out, you might give him a call.  For the stick I just bought a univeral pitman stick at the local fleet farm and cut / drilled it to match the old broken one.  Only not broken.