I use 15% for manual trans, 18% for these vintage Torquefilte or C4 autos (more for other automatics). I'm assuming the car above is automatic. 392 x 1.18 = 462.5. That's "the numbers" as I would figure them.
But it still doesn't take into account that on the dyno it is just the engine, often with an electric water pump etc. Installed in the car there is air cleaner, full exhaust, water pump, alternator and what not. It's like the endless discussion of gross and net horsepower. So it is much more than just 18% loss, realisitically.