I'm no expert on these, but from the prices I've seen for an old "B", that sounds a tad on the high side. It should be restored for that kind of $, in my opinion. You should be able to get a nice Allis CA with wide front for that kind of money, and it would have an independently operated PTO via a hand clutch, which the B doesn't have. I would try to get the price down. As for the blade, the B doesn't really have a separate frame, and the mounting hardware may have to be specially fabricated. I could be wrong about that though.
Bill in CO