390 stroker

a 318 has a stock bore of 3.91 add .030 overbore...you got 3.94....

http://www.allpar.com/mopar/318.html

they say it is 3.91......

and make sure you use this number for Pi..... 3.141592653589793238462643383279502884197169399375105820974944592307816406286 ...