need help determining what head casting

Can anyone help determine what set of heads these are? They came off of my 71 dart that had a 340 in it. The motor is not original to the car. The block is an 11*24*68 casting date.

Here is the casting number on the head. On the block mating surface side has a 2531894-C

Any help I can get is greatly appreciated.

Here is a pic: