1971 Demon with some coolant issues

I am leaning towards going this route:

http://www.rebuiltautoengines.com/dodge-V8_5.2_318-engines.html

This outfit is local and pickup would be simple. It looks like a 318 is $1,189 plus a $124 core charge. I want to set my self up with a platform that I can build a mild street engine from. Initially I was looking at the Mopar Crate 360, but I think this is more my price range (and speed).

Any thoughts on these engines? It appears they will work with you to customize the engine if wanted, are there any options I should look into? different heads? porting?

I will probably use an edlebrock manifold and 4bbl carb (600 or 750?). Thanks for answering all my questions.. this is my first mopar project.