What is this and why would it be there?

gzig5 said
They gotta machine the lifter bores and if there is any part of the block sticking out in line with the lifter bore axis from the deck on down, it is going to get machined. Right? I can't see why you would add these slots there on an engine that didn't have them? The lifter is .904 diameter as is the bore. What do you need a cylindrical relief for that far above the lifter hole? I The tie bars aren't that shape and the slots are deeper up by the deck. I guess the roller lifters are longer, but then that slot would have to be offset from the center of the lifter bore? Guess I'll have to look at the bare block in the garage and see if my feeble mind can grasp it.

Just guessing..... tooling clearance. I have thought in the past that maybe it was the head of the lifter boring tool, or the shank of the boring bit, that needed a bit of extra relief on a particular machine line. That could have been one or a few machines. Getting past the lip of the block and all the way down to the bottom of the lifter bore would seem to require a very long bit. A shorter bit or a stouter bit shank, would mean a more accurate lifter bore, but would mean the block needed clearancing for the tooling.

If you look at your bare block, place a lifter in one of those slots, and see if the radius of the slot is larger than that lifter radius.