You will find many Boss 302 blocks with cylinder cracks because there was a piston skirt problem with the original pistons which was mostly fixed by the 1970 model year. The pistons crack, come apart and crack the cylinders. There was a Ford recall on the pistons and anyone who had an engine break because of this got it fixed under warantee regardless of age, because of the recall. This put a lot of cracked blocks out there.
Also, I presently have a Mexican 302 for sale. If you're interested e-mail me for photos. It has no ridge on the cylinders and is presently at 4.000" ID. Has surface rust and no cracks.
wpasicznyk@crest-ultrasonics.com