Re: how much can a 3970010 block handle, it has the 010 high nickel casting
From what I've been able to gather a factory block is usually safe (with good prep, splayed 4 bolt caps, etc) to 600 horse. Have heard of a few that have gone to 700 or more, but it starts getting risky IMO over 600. Somewhere above 600 the factory blocks can split and lift the deck.
The problem is, different castings have subtle differences and even blocks with the same casting numbers are not 100% exactly the same due to date, core shift, over bore, metal fatigue / work hardening, etc.
Sonic checking can help find core shift, plugging the deck, filling the jackets, etc all help, but by the time you get into the expense of all the extra prep work you might as well go to an aftermarket block and not worry about it for a high HP application.
E85 racer and E85 carb builder
68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle