The holes should be 3/8 thread and 1 1/8 inch deep.I measured this off a original block when I needed to drill mine.I only went 1 inch deep in mine instead of 1 1/8 just to be safe.I did not want to drill to deep LOL
No they are 7/16-14 thread and less than 1" deep , I did a 69 block that I had that had the bosses but they were not machined , drilled or tapped . to do it correctly first you need to face off the bosses , i used an original machined block as the template to do my other block.