Bryan-
When you mention "alloy" block, I assume you want an aluminum block. Right? If so,
http://www.racepartsdistribution.com/index.htm is the retailer for Ford aluminum blocks. The 429 Al block is pricey - $4800. But it does save weight.
Bore and stroke to 532 ci., add some Jon Kaase SCJ heads and a Crane Cams mechanical roller (.718 lift) and you will instantly make 850 HP
Bill