Ford alloy block back in the day was extremely experimental. A 427 cast in alloy and then sleeved back to a 390 size bore, with small valves. Perhaps a bit to far ahead of it's time, nothing ever came of it. Of course GM tried alloy with their little 215 cid engine, eventually sold to Rover and that program ended. The Vega was up next, we all know how that ended, "up in smoke".
But the technology has matured over the decades, alloy is a good choice today. Still, I tend to favor the overall better strength/reliability of an iron block, with less fuss. In the long run, for a typical horse power build, I believe they are more economical, not as easy to warp or crack and can endure more "screw up's" (like overheating issues) in it's life span than an alloy block. My same reasoning applies to heads, even more so with heads. I'll take iron over alloy for greater endurance and long life potential.
Simply put, I don't have the deep pockets to get into an alloy block and would tend to worry more about something going wrong than I would with an iron block.