After some tests, I can say say that M42 (e30 and first e36s) not air-shrouded have a standard Bosch diameter of 14mm, the M44 (and newer M42s E36) injectors are 17mm of diameter where they fit into the manifold. So they can't be exchanged between these engines because the hole in the lower part of intake manifold is different in diameter. The impedance is the same (near 15.9 ohm).
M42 injector (not air shrouded, ->1/94):
M42 air shrouded and M44:
If we with M44s want to fit M42 not air shrouded (that are bosch standard size as other cars) or other bosch injectors an adapter is needed.
That's all. bye
Diameter M42/M44 injectors is the same? 
Linear Mode
