can itr exhaust manifold fit on a b18b1 engine?

yes, all b-series exhaust manifolds will bolt up to a b series block

But unless you have a p&n head and high lift cams an ITR header will lose alot of low end torque. I was going to get a Hytech style header but my tuner Xact Dyno (they do all the tuning for Honda Tuninh mag), showed me on my dyno chart where and how much low end power I would lose. 4-1 headers are great for high rpm power but not for low end power. I stuck with my 4-2-1 header. On a stock B18a/b the motor doesnt rev high enough and the cams are not agressive enough to make full use of a ITR header.