It's still SAE net iirc... More or less the same method they switched to in '72. Flywheel, full accessories and such. I know of no car manufacturer that measures at the rear wheels, although there are some cars (LS1's) that severely underated and put down around what their net HP "should be" to the wheels.
Brake HP is a loose term... Another word for dyno is brake. Term is used too loosely IME to be counted on.
Gross Horsepower: Absolute maximum horsepower at the flywheel, with no load or drag from auxiliary systems, such as the alternator, water pump, etc. Created in an ideal environment with precisely controlled intake and exhaust flow characteristics, this category is of little practical use.
Net Horsepower: Maximum horsepower at the flywheel, with intake and exhaust systems in place and accounting for load from auxiliary systems. This is what most automotive manufacturers publish as SAE net horsepower.
Wheel Horsepower: Measured on a chassis dyno, the maximum horsepower transferred to the ground by the drive wheels. It can be affected by gearing, with lower (numerically higher) gearing tending to indicate a lower torque peak. Considered the most practical measurement of usable horsepower.
The newer ratings aren't measured at the wheels as some think. They are measured at the flywheel with all accesories attached to the engine, just like it would be when it sits in the car. Our HP ratings were made without the alternator, fan, power steering pumps, and what not all attatched. The HP ratings on our engines are slighty higher than what we would see if we measured the power output the way they measure the new engines power output.
I would imagine it only being about a 10% loss in power running an engine with accessories than without. But it also depends on how many accessories you have attached. Isn't this discussion fun?