I think AndyF is right about the first link. That just looks like an old web link created when new blocks and engines were still available from mopar. The other links say they are using "seasoned" blocks. I have no idea whether they are on the shelf ready to ship or just made to order. If not, then there really isn't much of an advantage to using them over a local builder. Indy Cylinder Heads is well known, especially for their parts, but with mixed opinions. ATK engines, the last link, are sold by both Summit and Jegs. The 2nd and 3rd links I don't know much about. Was hoping that others could chime in. I have opinion here. Just sharing info I found.