The older bbc from 65 to 89 mark 4 block as the two spots on the block for the clutch pivot ball and over 30 years I used the 215 .396 heads was a cheap way back in the early 80s was done with a flat top 454 to get the CR up there and small chamber head bath tub chamber and like Jerry said you need to watch the size of I.d of ex seat as you can cut thru head casting can easly pass 470 hp with them heads I built 396/489 out of.them heads still would not say it cheaper to go ls but it close I done many nasty bbc.over the years and some very good running ls engines still the swap and dealing with some of the ls is no free lunch were to swap a 454 bbc in your nova is much less as gm parts.and many parts used can be found to make a 454 a bolt in job