I had this debate when building my 383....I'f you're going for that much power, you basiclly need upgraded EVERYTHING.
You wanna stroke NORTH of 351ci? "Theres an app for that".....Its called a 351 block. Thicker crank...bigger mains and the numbers you are looking for are more easily attained.
BTW My motor has an internal "0" balance crank 3.75" and 6.2" rods...
I personally wouldn't go with a 4.125" bore if you were using a power added. When I built my 347 I bought a NOS BOSS block. I wanted to keep it a 342 for added material between cylinder walls, but only bored it because of surface rust (the .030" kit was cheaper than a .010" kit).