By the time you are done messing around with trying to make up homemade blocks, you could just buy individual blocks @ less than $4.00 each (4 Wheel Parts) and know that they will hold up.
http://www.4wheelparts.com/product2.asp?imseqn=1399&occlass=P%2FA&cat=BOD
Also, Shaggy's sells aluminum blocks at Off Road Exchange.
http://www.4wheelparts.com/product2.asp?imseqn=1399&occlass=P%2FA&cat=BOD
Also, Shaggy's sells aluminum blocks at Off Road Exchange.