The big end shells are the same but the main shells on early blocks have a casting problem and the main shells have a +.4 on some of them ( Makes them wider I believe??).

So the sizes are (say?) standard +.4 and 0.25 oversize +.4 and so on. This would explain why they would sit out of line.

I had this problem with one of my old engines and the shells from ford with +.4 were mega expensive.

Have a look on one of the old shells and see, it should state the size and +.4

Hope this helps.