will any B-series header or stock exhaust manifold fit on my B18A??

 

yes.

 

Well, any manifold/header will fit on it but the downpipe may not line up with your cat. If you are looking for an exact fit it will really depend on what setup you have and in what car you have it.
If you have a b18a in a 90-93 integra then it would depend on the year of the teg. The 90-91 uses a different manifold than the 92-93 tegs because of a different sized catalytic converter. The downpipes are different lengths.

Later,
BR