hp ratings new way versus old way

trying to get back into the flow after years of being away. The new hp rating seems to cause confusion.

I read articles in Popular Hotrodding and Hot Rod magazine where the do a small block rebuild cheap and they get 390 hp. I recall the high end 'vette 327 small block advertising 375hp back in the day. It was fuel injected (yuck by today's standards) had 2.02 intakes valves and a nice floppy solid lifter cam. So when I see a 350 rebuild that is only 15 hp over what was sold stock 40 years ago I can't get too excited. But then this is where the rating confusion may enter.

I understood the new rating system accounted for an 'as driven' engine so the testing must include the generator, fans, A/C, stock exhaust, etc. Where as in the old days, it was just the motor on a stand with optimized exhaust and no belts to anything. This makes sense.

But my review of the mag articles it appears they are testing using the old stripped down method and not the new methods which makes me think "390hp - so what?"

But my real question is how many hp does adding all this stuff take? For example, I'm looking a building up a streetable LT1. The Y-body version of this motor is rated at 300hp. I am assuming this rating is the fully loaded method. Any idea what this same motor would be rated at using the old method? In other words, if I were to compare, using the same method, the old 'vette 327 FI (rated at 375hp) against the 96 LT1 Y-body 350 (rated at 300hp) which one produces more hp?

apples and oranges ... the new engine if same cid can make more power with less CR and cam. many places were things have came long .better heads. cam profiles . intakes. valves . valves stem size. seat angles. ring pack. roller cam more rpm better idle . less CR . better head chambers . .engines still get dyno striped down it.s how much stuff you want to hange off the front of the engine when it.s on the dyno