Well.... Yes and no. The non Turbo B-21-23 will fit if you shim a little and re drill the mount holes on the crossmember. The problem you will run into is with the oil pump pickup and the oil pan. you need to mik and match with the B-20 Pump pickup and modify the pan.
I'm not sure about the turbo being as easy. On the 1970 142 that my friend put a B-23 in, he had to trim and re-weld the frame rail slightly to clear the exhaust (stock ex manifold and pipe) However I have seen pictures of a B-21 turbo in a 145, but I think the motor was not installed at the same angle that it is in in a 240 series car.

john