Cab, my block from my little 451 was not filled and finally cracked, so I am going to fill the next one. This engine only made a little over 700hp but I bracket race most weekends from May thru September so it gets the snot run out of it year after year. The block was sonic tested but don't recall the numbers off hand.
if you want your rings to last like your old motor did do NOT fill it
The last motor I redid for a NHRA stock class racer( 3/4 filled1971 340 motor built by Greg Luneack(SP?) originally) wore a set of rings out on the dyno while testing cams and heads, less than 70 pulls
Those rings were back cut 5/64,5/64 and 3/16 oil rings
The dyno owner used his hand held infared thermometer to read the outside block temps on the dyno while running and after cooling it down for the next pull. The owners like to pull the car out of the staging lanes with less than 100 F coolant temps and have 110 to 120 F leaving the line so we where using 120 F as the starting point on all the pulls.
We found that with the head temps and upper block (above the fill) at 120 F while the lower block would be around 180 to 200 degrees depending on how long we let the dyno water pump circulate water through the motor :shock
It would take over one hour to get the lower blocks temps down to 120 F with 60F dyno water temps going in the motor
That was testing in the spring at night in the high desert part of the Mojave desert in Hesperia, CA with 60 F outside air temps or lower
I've seen a lot of RB blocks,413, 426 W and 440 blocks with crack main webbing, filled and not filled
No 400 blocks yet with crack main webbings regardless of the HP made with no fill, broken main caps yes
Cracked cylinder walls also
Your best bet is new race block to start with
