Can anyone tell me what's an acceptable blow by?

 

The crank case pressure is not measured in PSI its measure in( inch H2O). You will need a magnehelic gauge which will need to be plumbed into the crankcase breather cap. Ford also has a tool you can purchase but its not cheap. The test is done with the engine at least 158 Degrees. The engine is ran at 3000 RPM and the pressure reading is monitored for about 30 seconds. The average steady reading should be less then 10 IN H2O per spec.

If you are not planning to work on a lot of these trucks the test equipment would be an expensive investment at around 800.00 for the test gauge and adapter just to due your personal truck. It would probably be cheaper to have a dealer or shop that has the test equipment performer the test. I really can't see them charging more then 150.00-180.00 to preform the test. You just need to be specific on the test you want. Tell them you want a crank case pressure test. If they try to charge more then 1-1.5 hrs i would say there not being far. Them may try and charge a diesel Diag fee i really don't know.

 

Hose, ruler, water... No need for an $800 gauge for a one-off Inches H2O measurement. The weight of (fresh) water is the same everywhere and rulers are pretty accurate too.