There are a couple of aluminum Cleveland blocks being cast right now. One is from Arrow in Australia....the other is Mark McKeown's block.
Honestly, if someone wanted an aftermarket block, I'd advise them to spend $1600 for a Dart SHP block instead of spending $2500-3000 for an aftermarket Cleveland block. I suppose if someone has to have a period correct looking engine, then there's only one option though...
What keeps you from getting 427 cubes is the deck height. You'd have to use a 4.100" or 4.170" stroke and that just makes the piston way too short for street use. A 408C with CHI heads will make as much horsepower as most 427W combinations though. I guess some people just require the "magic number", but I think it's overrated...
I did a 408C with 208cc CHI heads (out of the box), their 3V intake (out of the box), 10.3:1 compression, and a very mild solid roller and it pumped out 575hp very easily....no fuss, no muss. The CHI heads are the only heads that I've flowed and the results were what the manufacturer said they should be....
If you can't tell, I'm very pro-Cleveland....haha