Having done many conversions, to me it boils down to this. Any bar must provide a position which allows the wrists to adopt a position without the tendons in the arms being twisted. By this I mean the hand should be holding the bar with the thumb facing upwards, which means the tendons are in a natural position. It is possible to do otherwise, but for any distance the blood flow will be curtailed by the twisting of the wrist and problems will arise.
What means you achieve this is up to the individual rider but I think the principle holds good.