Ok in 73 NHRA put heavy weight penaltys on big block cars. And even more on the Mopar Hemi's. This lead to a rush to smallblock Vegas & Pintos. Kinda backfired on NHRA as the Ford guys chose to run their powerful 351 Cleveland engine which had a "semi-Hemi " head. Turned out to be the winning combo. As 351 Pinto's & Mustang II's where suddenly everywhere. As an example here is s pic of Mopar racer Don Grother who sold his Cuda & built a Pinto. Still had his hauler painted in the Plymouht theme. Soon NHRA added weight to the Fords & that slowed them down so the chebbies could win again. Ford racer Bob Glidden was so upset that he built a Chebbie in 76, but decided to stick with Ford. The NHRA wouldn't let the Mopar teams run a smallblock Colt because it wasn't American made. So that was the end of Mopars being competitive Untill 79 when Gliden came out with the smallblock Arrow
It is funny when the NHRA tries to outlaw combos out of competition, and another dominate rises up, probably the worst drawback from no Colts was no development of small block heads earlier and more of it.
Roy Hill wins Darlington. Hill in his Hemi Arrow celebrating in victory lane (blue shirt) after winning the IHRA Pro Stock race at Darlington, SC. IHRA was a bit kinder to the Hemi cars and they had a fighting chance. Didn't dominate as they still had restrictions, but at least they ran well. What doomed them in IHRA was the Mountain Motors. The engines kept getting bigger & bigger & no one wanted to make a Hemi block that could go that big as the fear they would get handicapped if they got winning too much. Today there are a few 800 plus inch Hemi's running IHRA & are largely mid pack