My guess regarding the taper would be that they kept hitting the front cross bar with the bow so they raised the front end. Or maybe it was a drainage issue on their driveway... or even to facilitate splashing the boat at the ramp. I think I'd try to bring the bunks closer together and put some keel rollers just above and aft each cross beam.
Who knows what the previous owner was thinking? Its possible that he was a genius and that's why the rest of us are stumped.
The out of parallel issue could have been bad measurement, slippage over time or who knows?