455 standard bore built in the late 70’s, block is 73 but these look like a much smaller dish, marked in the face with “STD” and a Star with a O next to it..
Is the head off or are you using a bore scope device? If you could measure the depth of the dish in the piston, it would help as perspective can be difficult in 2D. With those caveats, those look like higher compression pistons. How far down in the hole are they at TDC?
Unfortunately, those are likely low compression pistons. I'd guess about 8:1 CR with everything else stock. http://www.buickperformanceclub.com/pistons.htm
I did the math and the dish is somewhere in the neighborhood of 36 CC. Big, long full skirts on these too, hang out the bottom of the bores. I was told by the guy that built the engine they were part of a rebuild kit, maybe TRW?