Climbhoser:
I wouldn't recommend them for below the bar setup. But then, I can't recommend any bars with limited hand positions to be set below the bars. The whole concept is to get weight off the hands, and, to position your supporting structure (hands, wrists, arms, shoulders, etc) so that they are in a relaxed posture for a majority of the time you are on the bike. Placing the bars above the saddle does require that the rider compromise on some aspects of efficiency for ther sake of tissue health and comfort. I set my NR's at about saddle height, with the grips angled about 10degrees down, or nearly flat. I alsom use a Brooks B67, which is designed to compliment a more upright posture.
Using an old school MTB or just about any modern bike will not set you bolt upright liike the old 3-speeds. That's because the 3-speeds were very much shorter in the top tube than more recent bikes.