When I pre-oiled the 6.5 in Sarah's Blazer, I left the valve covers off to check for oil at the rockers... This was the first 6.5 I'd pre-oiled, so I had no prior knowledge of what was normal... Just for background, all of the pushrods had been cleaned with brake cleaner inside/outside, checked for straightness and then oriented correctly before installation. Then the valve train was assembled. I had used chassis lube on the pushrod ends, ends of the valve stems and rocker pivots, and motor oil on the lifters as they were installed. Then, I squirted more motor oil on the rockers and valve stems (stem seal areas).
After having run the oil pump drive for quite a bit during the pre-oil stage (with the valve covers off)
I never did see oil at any of the rockers, even though the engine had been under ~35 psi of oil pressure all during the pre-oil stage. I puzzled over this for some time, a little concerned at first... There was plenty of oil/pressure at the turbo oil feed line. That line was capped off once oil flow was verified, so I could continue priming the oil system - thinking I could get oil through the pushrods and spill onto the rockers. Didn't happen.
I think the lifters need to be in operation - in a rotating engine for oil to be pumped through the pushrods. Didn't think it was possible for all 16 lifters/pushrods to be a problem... so I considered what I saw to be normal.
The engine now has about 900 miles on it, mostly at 60-70 mph. So far so good...
On edit... GM's recommended maximum cylinder overbore is 0.030", but we all know pistons are available in larger sizes. Personally, if the decision is made to fix that deep scratch, I'd consider having a sleeve installed in that cylinder that is bored to match the piston you already have. If nothing else, this saves the cost of new pistons and rings. This repair procedure was done for the 6.5 in Sarah's Blazer... due to the melted piston and scored cylinder problem. All this happened before I became involved with the Blazer. I don't know if that cylinder could have been cleaned up with a .030/.040 overbore, or if it required more. The Blazer came with a "new takeout" set of eight standard pistons/rings, which is what I used. If I remember correctly, the pistons came from a guy who had swapped the stock pistons for 18:1 pistons in a new/reman engine he was working on. So, this meant he could sell the practically new standard pistons to recoup some of the cost of upgrading. All of the Blazer's 6.5 bores and ringed pistons were mic'ed to produce the best fit - all were well within factory clearance specs.
This is the second engine I've been involved with that had a cast iron sleeve installed. The first engine was in our
6.5TD Power Project truck, which accumulated 300K miles before being sold. Based on these two examples, I don't see a problem with properly installed sleeves. The engine shop in Hamilton MT installed the Blazer sleeve. I'm not necessarily advocating for sleeves, just suggesting options.