So far we are very impressed. I ordered 1 of Summit's new SBC blocks in 2pc rear seal. We ordered a 4" bore block so that we would be able to insure the cylinders were straight and to GM spec. The guys put the block in the Rottler F69A yesterday and started to probe. Must say out of all the aftermarkett blocks we have had on the machine, the Summit block was the closest to GM print. Cylinder were only shifted .0015". To square deck the banks to spec it too .002" on one side and .003" on the other. Checking lifter bore location and cylinder wall thickness after boring and honing to 4.125". Main bore in the middle of factory spec.