My first 400 pump gas stroker motor was built with a 4.25 stroke crankshaft from Ohio Crankshaft company with a set of CAT brand 6.800 long BB Chevy H beam rods with a set of Ross dish pistons and a set of 906 iron heads that made exactly 9.25 to 1 compression ratio.
I put a custom(260@.050 intake with .420 lobe lift, 266 @.050 on the exhaust with .409 lobe lift ground on a 108 LSA grind Comp Cams solid roller cam in it. I put a stock type low deck six pack Eddy intake with a set of 1970 440 carbs on it.
That combination made 612 HP @ 5500 RPm and 644 Ft. Lbs at 4500 RPM and help my 3450 Lb. Duster run 10.69 at 124 MPH the first time out.
I race the heck out of that block, it had four sleeves and a welded up deck due to a head gasket blowing out the deck between #4 and #6 I did have a set of Mopar brand Ductile iron main caps and asset of ARP main studs installed in the block to start with
I ended up switching heads and increase the stroke to 4.300 to get the compression up and the car ended up running a best of 9.993 at 134.6 MPH with the air cleaner on and full 3.0 inch exhaust to the rear bumper hook up
My message is the stock 400 blocks will take a lot of beating with decent (under 800 HP) amount of power as long as you get it tune properly Don't let it ping or detonate ever I did let it do that a little on the first combination with the iron heads and it made the main caps fret and walk a little, I dress them up with a good flat file and ran it a lot more, no failures yet as far as I know