Im pretty sure my block is a 80 4 bolt main block because I checked mortec when I got the block. I did a look up for the block front pad codes and discovered it was a service replacement block for a 80-85 truck. I was putting on my intake today and noticed it had two bosses in the liffter valley area about 3/4 inch high and one inch round. Im wondering if this would allow me to put in a roller lifter spider for the roller conversion. I know most oem lifter spiders have three holes where they mount to the lifter valley bosses. I thought it was strange that my block had two bosses in the center of the lifter valley that I have never seen on any pre-87 block. Has anyone seen one of these blocks with the two lifter valley bosses before?