I have seen both ways on the 400 blocks starting around late 1968-1969 time frame.
Personally my favorite 400 block is the 'lowly' 67 2 bolt main (non drilled for 4 bolt mains) block as you can add splayed caps fairly easily but $$$.
The other benefit is that the 2 bolt mains will be fine for many levels of street cars and the main webs are a lot stronger without the extra holes drilled in the block webs.
You have run across some interesting stuff like the '73 455 that had 4 bolt mains installed on it out of a Grandville. When the cars were going down the line and the 2-bolt main 455 block engine was not right there at the moment, the 4 bolt main block engine got installed.
Tom V.
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"Engineers do stuff for reasons" Tom Vaught
Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward.
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