Re: 396 bored to 427?
From what i understand the 961 bbc was the only block that GM used for production 396 & a limited amount of 427s in late 1965 into 1966 when the 427 introduced . (maybe 67 too but not sure of that)
BTW,not all 1965-66 961 bbc 396 & 427 blocks were able to handle the larger 427 bore,they need to be sonic tested 1st.
Another supposed way to confirm if 961 block was able to go to 427 bore was if you can't get a std size pencil inbetween the cyls in water jacket when trying it thru freeze out plug hole in a 961 bbc block it meant the cyls were thicker alowing for the 427's larger bore.
But i have never expericned that for myself ,i had a 66 961 spare motor (396) with 840 heads approx 12-13 yrs ago with L78 intake,steel crank,dimple rods with large bolts,etc.
I sold it to a guy restoring a 66 chevelle ss 396/360hp 4spd for $600,paid $125 for it 10yrs prior so did ok on it.
Other then the 961 block other 396/402 blocks would not normally safely handle the larger 427 bore when using a stock 396/427 crank /stroke to achieve it & not a stroker crank to make for ex a 434 bbc stroker motor from a 396 or 402 bbc block.
1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)
2009 HD ELECTRAGLIDE CLASSIC ULTRA (GOT 11/14 W-9,700 miles)