5.2 Magnum Piston Question

They look like 285AP or possibly silvolite 1266 pistons...if they are, they're a low compression piston with either a 1.72 or 1.74 CH respectively. Assuming all other measurements are indexed and nominal, those pistons would be 0.102" in the hole at TDC. Even with magnum heads, that puts your compression approx 8.2~8.5:1