I have been told by 3-4 'big name' pro shops that after market alum blocks (not factory blocks) are really a no-no for the street. Reasons: (1) the constant heat, cool, heat, cool, partial heat, completely cool, hot to partial cool and back to hot again, etc., etc. over time (they all said that means within 5K miles or so) will cause the cyl bores to 'go oval on ya'...and the mill will start blowing oil past the rings. Why? Because after market blocks don't have the extra 'webbing'/'stiffening' that the factory blocks do, they're just made thicker...and they tend to twist/warp/distort because of it; (2) Alum blocks create more engine compartment heat than an iron block due to more rapid heat dissipation...& therefore more heat transfer to the pass. compt (and wherever else!), and, (3) an all alum engine will make and 'broadcast' more internal engine noise when running. An iron block doesn't let as much internal noise 'escape', if you will.
I have an dart aluminum block with AFR aluminum heads, just clicked over 12k miles in CA for which some of them where 3 open road races with average speed of 110 MPH for 118 miles, 2 track events and at least 100 BONZI runs under my belt. So you mean to tell me that this race motor driven on the streets is not going to last? How many miles on your car?
This is going to start a pissing contest so you do what you want, but use common sense and not rumor has it. Have a great day over and out.