Engine block filler

As I plan my next engine build a Pontiac 455 I am considering partially filling the block. Many say it improves the true of the cylinder bore and improves the cooling characteristics of the engine. Anyone have any experience with this modification.

 

Are you going racing? Or is this a Street application?

 

unless You're going racing, it is really a bad idea on a poncho.

 

I ran a 455 at Bonneville. Filled the block to the bottom of the freeze plugs. Bored very round and sealed better than the previous block with out "Hard Block" Since my Vintage motors don't have water jackets all the way down the cylinders and seem to have lasted 70 years or so I guess it's OK to do.