I still think Bill Jenkins built the first one , to try to keep up w/ Sox-Martin . I read about nhra inspecting it as the first one , back then . All the others followed suit to keep up .
In late 71 Mopar and others went to NHRA begging for a safer full tube chassis and was told absolutely NOT. So in 72 Butler built the Mopar Missile (to Mopars specifications) with OEM front unibody frame rails / modified K frame and like the Motown Missile, rack and pinion steering. They go to the WinterNationals and Jenkins shows up with a full tube chassis Vega. From what I understand the majority of the field should have been DQed, but NHRA had a race to run and a field to fill. So when Butler built the next race car (Butch's 73 Pro Stock Duster)...it was game on.
This is fairly fresh in my mind, about 3 weeks ago I had this same discussion with Butch as we discussed how trick the chassis on his 73 Pro stock Duster was.