I wasn't commenting on the design or manufacture, I agree with you, along with just about everything else Toyota designed for the 80 series, the wheels are beyond what could be reasonably expected. I wasn't aware they were spin cast (I thought I remembered someone claiming they were forged, which I gave serious thought to throwing a BS flag on). That makes them more homogeneous (no voids to speak of), and it's the most expensive high volume production casting method.
I simply meant to say that casting, no matter what process is used, results in variable material volumes, thus variable finished weights, especially when polished surface finishes are required. In a wheel, it's not critical because it's a rolling load completely supported by the ground. The only real consideration (aside from structural strength and integrity) is rotational balance.