Hi Chet,
A friend of mine who is not internet active, I see him 2 or 3 times a year but he does interesting things to convert tenor banjos to 5 strings. The tunings take on a whole new variation but they sound great.
To play these little guys, you can't tell any differenc other than every thing is scaled down in size. He has glued a narrow strip of wood and finger board to widen the finger board to accomadate the fifth string and adds a 5th stg tuner. He might even refret. They are beautifully done and there seems to be a good number of used tenors still available. I know he sells some of these banjos and can only provide you with a phone/address on the private side of this forum.If you are interested, let me know.
Mudjack