Random lifter rattle
He said that the sound can be random. Truth is, if he just bought the car, he really doesn't know what is in there. Or, cam bearing off? Went through something similar to this with my '69 340 Dart that I bought last year. I tore the motor down over it, ya never know. Clattering lifters are not that common, not that remember.
Hope that you have better luck.