I don't think the Chain drive was to reliable,,I remember that the engine torque would put enough slop in the chain to throw the valve timing off and Puke the motor, later a gear drive was available,
FYI Mickey Thompson Developed Hemi heads to fit the SD and had Pontiac decided to stay in racing you could bet by mid year there would have been a few out there a year before Dodge re-intro'd them( a few of these engines still exist)Tony Nancy,,that name brings back memories