Believe me your plans will change a thousand times before it's done, that's why I say go ahead and get the good stuff down low like forged internals and a good computer balance job, it sure will save you time and money later when the plan changes. I started out building a mild 468 for my camaro drag car but it changed to a 496 and well after almost 6000 dollars into it with seemingly no end in sight..lol but it will be a screamer if I ever get it done.
I'd hate to recomend a cast steel crank but it seems to be the direction your leaning on. That same vender I used sells a cast steel set up for about 900. Browse the engine parts section in drag race engines and you'll findem. GL, Charles