those are steel correct ? NASCAR heads They were never used in any of the A list pro stock cars
D4

Alternate cylinder heads for the 426 race Hemi. Initially developed in 1969-1970 using the same intake valves and ports as the D1 but with larger area, higher exit and straighter exhaust ports. The first D4 head power runs on May 1, 1970, and the 426 Hemi generated 641 hp.

Mullinens made some aluminum copies D4-A