426 stroker kit

I'm going to build a new stroker motor for my Challenger. I like the 4" crank (I think both Scat and Callies offer one). I have a new 6.1 block with stock bore and factory hone so I have to work out the c.i. of a 4.055 bore with 4" crank. I think it's more like 413 or so. An alternative I'm considering is an aluminum block at about 4.125 with the 4" stroke. I think that's closer to 426 or so. Expensive block though, unless I can score a good price somewhere. With the cast iron block, I'm not comfortable going beyond a 4" stroke for longevity. You can go more on the aluminum block because of the steel material used for the sleeves...