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More Low-End Output

The suggestions I got for increasing the low-end (2000-4000rpm) output 
of my 1985 318i 5sp with 57k were:

1. Get a different car:  I see this as my last option, but nevertheless 
   a valid one.

2. Drop in the engine from an E30 325e or 325i.

3. Increase displacement to 2.0l, by replacing crankshaft, pistons, etc.  
   Probable cost (done by a mechanic): $3,000-3,500.

In reference to 3., I believe it may be a good option for somebody with 
a worn engine which is going to be rebuilt anyway.  In my case, it does 
not seem worth to tear apart a 57k engine, spend that money, and 
probably end up with only 11% more torque (assuming linearity to 
increase in displacement).

With respect to 2., I wonder whether an increase from (max.) torque of 
103 lbs-ft that I have now to the 170 lbs-ft of the "e" engine or 164 
lbs-ft of the "i" engine would also require to have to change clutch, 
gearbox and differential.  With likely additional mods required like 
larger radiator, switching battery to trunk, etc., I believe option 1. 
may end up being more practical than dropping in a 325 engine.

However, this made me think of dropping in a 16-valve 1.8 engine.  Max. 
torque is 127 for the E30 version, 129 for the E36.  Sounds more likely 
to be withstood by my drivetrain.  I presume things like heat 
dissipation and others are also more likely to be handled with less
problems compared to 325 engine requirements.

Does anybody know how feasible and easy it is to put a 1991 (E30) 1.8l 
or an E36 1.8l engine into a 1985 car ?  Any advise on what would need 
to be adapted/modified ?  What would be the best way to find a used but 
good condition such engine ?

Moreover, is there any other simpler method to increase low-end output, 
i.e. some bolt-on addition ?  I would be happy even if it was just 10% 
increase, and would be willing to pay $300-500 for that (switching chips 
would have fitted this strategy).  I am also willing to invest 
$1,500-2000 for an increase of around 20-25%.  

Are any of the following possible solutions ? :
 
a)  A blower.  I believe a turbo-driven one would still give 
more high-end than the low-end emphasis that I want.  Would a belt 
driven blower (supercharger vs. turbocharger) be better at increasing 
torque at low rpms?  If that were the case, any ideas where I should 
look for such a blower for this engine? 

b)  I remember some time ago a posting about improved performance by an 
engine management system for the 320i with K-Jetronic.  Any similar 
system for L-Jetronic ? 

Thanks for the help,

Andres
ajaime@domain.elided