I'm late to the party, but the 360's 2.81" main journals have to be machined to 2.5" to work in the 1962 - 1966 poly 318 that uses the LA273/318/340 crank. Then there's the external balancing to deal with. By the time a machinist does all the work, it's easier and not much more money to buy a Mopar Performance internally balanced 2.5" journal 4" crank when going the 390/402 stroker route.
www.poly318.com has a comprehensive parts interchangeable section I use, and the website owner Justin is a very approachable guy, as is Gary Pavlovich.