[JoeC]

Not many 1967 or 1968 TH400 427 Yenkos have been found so hard to say how they were built.

In 1967 Yenko ads show the 427 TH400 car as 410hp with hydraulic lifters.
In 1967 Yenko converted SS396 325HP TH400 cars to 427
It is not clear how the engines were equipped
They could have used a 390hp L36 short block or long block and called it 410hp.
Not sure if they used the Q-jet or changed out the intake and carb for a Holley

In 1968 Yenko ad shows 427 425hp TH400 cars.
Most likely converted from an SS396 325hp TH400 but it is not clear if they used hydraulic lifter or solid , oval port heads or square port heads , Q-jet or Holley, to get the 425hp.
It would be a stretch to use a L36 390hp and call it 425hp

I have not heard of any SS396 325hp TH400 Camaros with the COPO 9737