From poking around it seems that the 185 lbs for a 428 is about right. The original cast iron 427 blocks are around 200 lbs. per the Genesis site. The Pond aluminum block is about 120 lbs and the Shelby aluminum block is 125 lbs. The Genesis cast iron block weighs 230 lbs.
http://www.shelby-cars.com/Shelby_Alum_Block.htm
http://www.genesis427.com/Blocks1.htm
http://www.robertpondmotorsports.com...gine-block.htm
Good luck with the search and build.