Awesome # s !!
The 727 actually has less moving parts so I doubt it loses much power .
Converters do eat power & driveline loss around 20% sounds close
Drag strip # are not really more accurate as there is a lot of variables there too , traction , shift point RPM but MPH can be somewhat more accurate
I use 18% driveline loss for stick shifts, 20% for automatics. 4sp autos will take more power to run, same with an add-on OD unit.
The comments on drag strip performance is a bit vague at best, and at worst incorrect. If one is trying to see how a given engine performs in a given car there is no more accurate way than taking the weight of the car, the miles per hour it reached, and the length of the timing lane (assuming some tracks are 1/4 mile, some are 1000', and some are 1/8 mile) and doing the math to achieve truth and accuracy for your package. ETs may vary based on everything. The Moroso slide calculator has been the standard since the 60s because the physics never changes even if technology does. That's because whether you're talking a model T or the USS Ronald Regan it always take "x" amount of torque to move "y" lbs of mass to "z" mph over a given distance. Once you have the torque figure, you can add time ino the equation and get horsepower.
Engine dynos, on the other hand, are entirely mathematically driven and results are based on everything including how much equipment is supplanted by the dyno cell, the temperature of the cooling loop, the construction of the cell itself, the operator, the sampling rate of the dyno's software, and the operator themselves. Dynos are exactly like flow benches: they are tools, not truth. You can't race them, and they are not a true picture of "your engine" in "your car". If you want a little beter idea, find a relly good chassis dyno place and have it dyno'd there. At least then you take into account accessories driven by a belt, actual enine temperatures, restrictions in intake and exhaust systems, and driveline loss.
