On cars 1971 and older they used "gross HP" rating, and after that they used "net HP" rating. So a 375 HP 440 Magnum suddenly became only 275 HP, which more closely matches what they use today. No net rating for the 426 HEMI, since they stopped making them in 1971.
And as already said, with today's tire technology, that same HEMI car would run mid 12's. A lot of HEMI cars came with 14" x 5.5" wheels, WTF! A 6" wide tire is not going to do much.
Actually, there is a whole Muscle car drag racing series where they have to run the 60's & 70's cars on the bias ply tires, and they run in the 11's and 10's with very minor mods, and hook up pretty well. But I am sure the bias ply reproductions of today are better than the originals.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles