4cyl and 6cyl coupes, sedans and compacts came with 80 amp alternators. Only 6cyl convertibles came with 140 amp, 4cyl convertibles came with 80 amp. A simple realoem search confirms this:
http://www.realoem.com/bmw/partxref....ur=&series=E36 Apparently, up to 9/93, some 318's came with 105 amp alternators:
http://www.realoem.com/bmw/showparts...24&hg=12&fg=20 And the pulleys between Bosch and Valeo have no impact on whether the alternator will work or not. Either way, it has to interact with the pulleys on the other components such as the water pump, power steering pump and crank pulley.
I don't think they made a 140 amp alternator that will fit the 4cyl engines. I'm fairly certain that 6cyl alternators will NOT bolt up to the 4cyl engine.