.030 5.9 magnum

I have a question, and before I start let me just say that I'm not trying to come off as rude or anything. There's no way of knowing your experience level, so, I've got to ask. How exactly did you come to the conclusion about the motor being already .030" over? Did you measure or possibly see a stamp on the piston that said it was 4.030"? The reason I'm asking is because if you're just going by the fact that you can still see the crosshatch marks in the bores, then that is not an accurate assessment. It's not uncommon to see an 100k+ mile magnum with good very visible crosshatching, a testimate to modern fuel injection, low tension piston rings, better machining processes, etc.

As for running 12's you should be able to hit that goal fairly easily. Myself as well as a few others (LXGuy comes to mind) have run 11's with some very basic builds. My best 1/4 mile combo was a stock 5.9 magnum (cracked heads and all) with a baby rv cam, an Edelbrock Air-Gap intake, Holley 850dp (a little overkill), and block hugger headers (which, lets be honest here, don't really count when compared to longtubes) ran a best of 11.87 @ 112. I know I know, different car, I've got an aero as well as a weight advantage, but LXGuy (check out http://www.magnumswap.com to check out his car) has run both quicker and faster than me with a combo not much more radical. I think just a bigger cam, some EQ (Iron Ram) heads, a well sorted drivetrain, and presto, easy 11's.

The point is that it looks like you're jumping in deep (bottom-end work is not cheap) to build a motor to run a number that is easily attainable with a simple bolt-on magnum. I'm not trying to talk you out of anything, but just kind of putting things in perspective. It looks like you've got a good plan with the rear-end swap. What trans are you planning to use? Also, whatever you do, DON'T SKIMP ON THE CONVERTER. It can make or break your combo.