I didn't go read the linked thread, but based on the original post here, I'll say the guy is somewhat correct. BUT..it also depends on what combination you are talking about.
The engines built in the day all showed advertised, gross values. Yes there were a lot of advertised 10+ to 1 engines, for static ratios. Dynamic cranking ratios were likely all less. Horsepower figures were also gross numbers at the crank, in ideal conditions, with no accessories. Install a 335 horse engine in a car and subtract 35% of its output for accessories and drive line and yes, your down around the 200 mark, plus or minus some depending on the actual configuration.
Now, there were still some killer combinations from the day that were far and above the 200-250 mark. However, not every muscle car from the day was Hemi car or a shotgun Ford or LS Chevy. By far, the majority of muscle cars were just average big blocks. At least for a few months and the new owners started tinkering with them.
The engine shoot out show mentioned here also isn't accurate. The builders of that Hemi have admitted it wasn't exactly a stock unit, but rather a FAST style set up. I love mopars as much as hte next guy, but a 700 HP STOCK Hemi? Sorry, don't buy it.
So look at your time slip at your next trip to the track. Your mph figure will tell you pretty closely how much horsepower is at your wheels. E.T. is how well the combination of engine and chassis are working together. This is why you see some combos that do lay down big mph, but don't have the fastest e.t.