I don't want to start anything, especially with a guy with a gun :)
But...I don't believe "flywheel" HP is an industry standard term.
Gross HP is what most aftermarket engine builders use and what auto manufacturers used intil 1972.
Net HP is what was used after 72 and accounts for all the accesories that sap power.
A very sketchy conversion factor is plus or minus 18%. (I use 20% because the math is easier).
Going to rear wheel HP, you lose another percentage at the trans.
Again, sketchy conversion factors are 15% for a manual and 20% for an automatic.
Taking that +- 245 NET HP figure for the 5.9, and putting back the 20% to calculate an estimated GROSS number (so we can compare it to the figures for crate motors, etc) yields about 310-315.
Subtracting the 20% (from the 245 NET number) for the auto trans will give you that 200 RWHP number.
BTW, I used an accelerometer to measure a backroad 1/8 mile run, and used a whopping 85 RWHP!!