Darryl

That's the way I'd go, 4.07 x 4.125 is 429 cubes.

I'd put a .600 ish lift ~252/256 @.050 Bullet SR with 10.5:1 on 108 in around 104 and a ~3500 stall/4500 flash 9.5 vert. I'd prefer a built low gear set 904 to a 727 with your gears but that's just me the 727 would be worry free though.

1 7/8" E body TTI's and a pro systems 1000hp on a Victor 340 should still have awesome roll on torque and start pulling hard around 3300 and peak around 5800 and rev to 6300 or there abouts.
The extra cubes make up for a little less compression and cam compared to the 408 but it'll be available sooner (where you want it.

A quick footnote....the one reason I'm so big on the torque curve is that people usually (sometimes suprisingly) figure out that when you have a broad torque curve (which is roughly 85% of peak torque) spanning over 1/2 your total powerband, you quickly find out that you have such a wide sweet spot that you don't have to worry so much about getting the converter exactly right (you can go a little tighter) or hitting the shift points just right, it just makes the 'stroker experience' a lot more fun to drive, which means you'll want to drive the car more