340 or 408?

Well, no, it was a 4" stroke. This is the Small Block LS7, not the old BBC 427. That's why I mentioned the fuel cut-off speed of 7200 rpm. You are correct the old BBC 427 had the shorter stroke. The Small Block bore spacing did not allow for that old BBC bore size!
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Yep. And the head on that engine is probably as good or close to it as a 990 BBC head.

Put lesser head on it and see what it is.