Oversize Lifter Required

It is on the front right top of the block near the serial number. It is more a laid over rectangle. Somewhere there is a decoder for the marks and it shows the diamond.

So how did my '69 340 work OK with regular Comp lifters?

BTW, I am assuming the guy put in Comps as I have not taken the motor apart since pulling it. I am leaning toward selling the motor complete / running.