The scarcity last Summer for the World blocks made me look at an aluminum block for my 540 build. The only real downside I heard was that unless they were filled the bores would not stay round and true. I can also tell you that a filled alum block with a race size radiator will get pretty warm if you are just driving around at 45 MPH in 3rd.
I've been running a KB for 10yrs since I got rid of my Indy POS. You don't have to worry about the bores being out of round on the KB and my block is not filled.
