Touring conversions evolved over the years,Davids is the later (and more practical) the earlier was a single arm with 1 Cyclo and 1 Benelux idler. Also they did not as much accommodate a large freewheel as much as tiny front rings. Shimano/Suntour and Campy Rally allowed large freewheels (I think I have some 36t Shimano cogs out in the garage) Most of the basic 1970s Japanese bikes were delivered as a 52/42 (or 40) with a 32t rear as mostly standard. Bikes from the 60s tended to use a smaller rear freewheel but with a 52/36 front set up(''Alpine Gearing'').Derailleurs on these were almost always Huret or Simplex
Bob Freitas who got a little wet yesterday on his way home but the weather was cool and dry most of the way
BOB FREITAS
MILL VALLEY, CA USA