Well filling the block is great provided it HAS NOT beenmachined already. IMO it is a very good idea to ad some stability to the bores. Some of these block can be really thin on the thrusts. The girdle, iMO is debatable. Dont think it will hurt much but not sure how much they halp. I have run low decks with decent power and just done a couple of things. One is aluminum caps and rods. Next keep the bobweight as light as you can, how light well that depends on application. Lastly keep the thing from detonating and it will give you many years of happy service at 800+- hp..

Oh yeah let the flaming begin

Oh yeah an aftermarket block does not necessarily mean no cap walk...Been there done that, ask Greg I think he will concur.