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Paul,
I agree that reducing reciprocating weight is beneficial for horsepower. However, there are a lot of more important things that take precedence over the budget.
Question, because I really don't know: Why do late B20s have more reciprocating weight than early ones? Where is it?
Why would more mass bend a properly balanced crank sitting if properly aligned bearings? I don't see the dynamics of this, unless harmonics enter the picture.
As for heads, ports don't need to be all that big to take advantage of higher displacement. It's more a matter of combustion efficiency -- how much energy you get from a charge of air/fuel -- than of sustained flow. The quality of the burn is just as/more important than the quantity. That being said, with a well-matched cam and header/exhaust and some resonance tuning of the intake, you can get excellent VE without huge ports.
I'm running 93mm pistons, heavy "M" rods, big heavy valves, a B20F head with ports that still match the OE manifold gasket (although they have been reworked considerably for shape), and I can tell you it goes just fine, tolerates 7000 rpm no problem, and gets better gas mileage than a stock B20 when driven at similar performance levels.
YMMV...
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