This practice is still very common with drag race motors. Modern racers use a product called HardBlok, among other products. I have heard of folks using partially filled blocks on the street, but I think you've got to try some out to determine how much fill you can get away with. Also if there is not enough fill, the results in cylinder wall stabilization will be minimal. Usually, this is considered a race-only mod.
See
www.hardblok.com
The blocks you refer to are likely great for drag racing. May be OK for road racing. You could contact a reputable 427 builder to discuss how much block-fill is still streetable.
BTW, I doubt a cement-based product can be cooked out, but you could try it.
My $.02