I. D. heads
Those 906 heads are the correct heads for that year of 440. The 906's were used on the 68-70 383's and 440's and are most commonly used when building a good street-strip car. Nowadays you have to have hardened valve seats installed to run them on no lead fuel but other than that they were one of the better flowing stock heads that mopar put on their high performance cars.
Terry R