I am only pretty sure, but not 100%
The seller described it as draped, so it might be a B4.
if you look closely, the right shoulder seems to have pteruges, which B3 does not have. It also looks like the rivets at the top of the cuirass, near the neck, are visible; which B3 also would not have.
Hopefully when I get it, I can get a better picture.
I don't think that the picture you show as B3 is really a B3, or it is certainly ambiguous.