Here's a pic of the factory push rod which shows where to lengthen. Make sure it's a good weld and that it's straight when your done.
Sorry about the quality of the pics. I've had a couple different push rods made, the first I cut and welded the second was made by a machine shop.
Somewhere I have a better pic that shows them all side by side but can't find it right now.
Making the push rod longer will give you a bit more travel out of the slave but it will also raise the pedal about an inch ... it'll take a bit to get use to it.
Just an FYI, Sachs is a ZF company and is OEM on our trucks.
In the last year I've bought ...
Two complete hyd. sets from Ford
3 Sachs + 1 Brute Force master cyl + 4 Sachs slaves from Rock Auto.
They are the same parts (even have the Ford logo) just cheaper and available individually.
Master is about $50
Slave = $40
Complete system from Ford is about $200
If you find out that Woodruff Diesel or anyone else has an upgrade kit, please post an update.