Can't just give you a from the hip length however I can give you this advise.
Besides all the angle of the dangle BS. The one thing I look for is the contact patch on the stem through out the lift cycle. I usually put some blue dykem on the stem and spin the cam through its cycle. the contact patch should stay centered on the stem. If you are not centered you can change to a shorter push rod to move the contact patch away from the rocker stud or you can lengthen the push rod to bringe the patch closer to the rocker stud.
No matter what lenght any one tells you always check the contact patch!
Most performance places sell a adjustable push rod you can buy to mock this up. However I made my own with a coupler nut and a bolt.