Well for some insight on the B series engine go here and it will give you some knowledge on it
http://web.tickle.com/tests/uiq/inde...=banemedia1&z=
It depends on what kind of b series engine you wanna get and how much are you really wanting to spend...They can range anywhere from $650 on up $2,000 if not more.
Now about the engine swap I am no one to tell you about that but I am pretty sure Kai or JaJe or one of the others would be able to give you some info on that!!
Hoped I helped!!!