Push Rod Single to Dual Conversion

How do I know the original push rod is the correct length?
After the brake pedal is parking correctly; and after the brake-bleeding is done; You should have a hard high pedal. BUT
The pedal should do nothing in about the first inch, during which the pistons are self-adjusting in the M/C. By stroking the pedal rapidly several times in a row, you can pump extra fluid down the line and MAKE the pedal hard and high. But when you release the pedal, and wait a few seconds, that fluid should return to the reservoirs, and the pedal should again do nothing in about the first inch.
>If the pedal stays hard and the brakes are locked, then the fluid has Not returned and the compensating ports are on the wrong side of the pistons, because the P-rod is too long, or the pedal is not properly parked at the top..
>If the brakes do nothing for MORE than one inch, and /or the pedal does not return to the top, then the P-rod may be too short.