You know, I know everyone here is dogging aluminum, but I will say that I have one bracket 347 in a car, built from a later 5.0 block. It makes 540 hp here, guy launches at 5500, shifts at 7000. Car runs 6.90's in the 1/8th. It's been built for 10 years, had to refresh it 8 years into it because of a bad power valve that didn't get noticed. It's got a DSS aluminum girdle, main caps and bearings looked perfect on freshen up, with a couple hundred passes on it.
Either that block is a stout one or the aluminum actually helps with harmonics in that situation.
I do know that the big block Chrysler guys always put aluminum main caps on their iron blocks for higher end engines.
To the OP, if you do build one, try to make it with as least amount of parts as possible, as the block does have to be align honed with it on there. If you have a ton of parts, spacers, jack screws, etc., etc., then it makes it harder to duplicate the housing bore with each time you remove/reinstall.