After exhaustive research on this issue, I've discovered the following:

1] If using a stock Bosch or Motorola/SEV alternator, mounting on the left side of the block will indeed interfere with the steering box.

2] Left-of-block mounting *might* work if one used a modern, tiny alternator, say, out of a small Japanese car. My budget does not allow for such experimentation.

3] the bolt through which the main alternator bolt passes goes through two tabs on the right-of-block bracket, and only one on the left-of-block bracket. I would believe that to be a significant drawback, although it has obviously worked on thousands of RHD cars.

4] It certainly is feasable to fabricate a mount that would bolt to the same bosses that the left-of-block bracket uses, but place the alternator itself 25-40mm higher, thus alleviating the steering box interference. I however, lack such fabrication skills and equipment.

5] Until I can find a picture of the a/c compressor mount for LHD B20, I can't say if/how that might be used for an alternator instead.

6] For now, I am stuck with the alternator mounted to the right of the block.