Re:
You can work out the cable pull ratio for the Simplex derailleur to see if it's anywhere near anything on the charts.
1. take off the chain
2. line up the derailleur underneath the 2nd smallest sprocket (this will ensure you have tension on the cable)
3. put a piece of sticky tape arond the gear cable and another one on the downtube lined up with the one on the cable
4. move the gear lever until the derailleur is directly lined up with the largest sprocket
5. measure the gap between the 2 bits of tape
The derailleur will have moved 22 mm assuming you have a standard spaced 6 speed block. 20 mm if it's a compact block.
Divide 22 by gap and you've got the pull ratio.