[Ant]

Modify the position of the pin in the wiper motor, its dead simple!
Get an old wiper motor and experiment with moving the pin out to whatever the sweep you require, by drilling etc.
Also there are different gearboxes (cogs and shaft the blade attaches to) some have smaller cogs, if you have dare I say it Austin Allegro Vanden Plas (heap of sh*t) they have the smallest cog gearboxes.

These wipers worked alright on many cars over the years, but people get them and dont take enough care when mounting the motor and gearboxes and end up with the solid outer tube with "S" bends, they work much better with these tubes on a single plane!
I have always found the wipers travel to far, maybe when I actually test this setup with 110degrees etc I will be doing some modifying!