I have just about every RF adapter known and have never seen a SMA-BNC 90 degree adapter. I have a couple dongles with these ends but that wouldn't help with a side antenna.
I would suggest the Uniden SMA-BNC adapter (available at various dealers) along with a BNC antenna that has an angle. I don't like putting 2 adapters together, that looks wonky and can introduce more loss.
You might want to consider using one of those SMA mag-mounts on the HP-2, put the antenna on a metal file cabinet, shelf or appliance withon 12 feet of the radio. They have a very thin coax and hide well. It would usually work better than a portable style antenna.