Some guys on a budget want them.
Some regions of the U.S. are pretty lean on old cast iron cylinder head cores.
I ran a set on my 69 RR, added the 1.74 exh valve, bowl ported them with the MP templates, gained 2-3 mph through the traps.
It ran low 13's @ 105 mph. Just a warmish 383 B-motor, 833, 284/484, TM6, 750 AFB, 4.30:1, 10" slicks, 1.99 60'.