gerg here is your answer,ford wanted a 400 size engine,because chev had one and wanted something inbetween the 351 and the 460,if you look closely you can see 2 casting bosses that are identical to the normal cleveland and windsor mounts,but they are undrilled,because they used the bottom of the normal cleveland in the mould but ford liked doing weird things and the other side only 1 undrilled boss is there and not the other one which to this day is still a mystery,there is only 1 holy grail 400 that has both sides drilled to fit normal cleveland mounts and is highly sought after even in the usa,i thought thats what this block was but its the next best thing and is still extremely rare a unicorn 400,so far the stripdown is 100 PERCENT good with block in gc and i honestly think i might be able to use the pistons that are in it,i will let olm8 at the machine shop examine them just to be sure ,i mean this aint gunna be a big hp motor just a mild stump puller with the stamped steel rockers and very mild tourque cam,but wait there is more i have found a set of NOS std matching 8cc pistons still in the box from 1971,so either way we are on a winner,olm8 will use the round mic thing to check the bore i suppose first but i reckon all it needs is a tiny ridge cut maybe at first inspection.