Glad you found a builder! Post up some vid from the dyno room when you can!
I don't know why everyone makes it sound so hard to build an affordable BB stroker. I remember when one of the mags did a write up on a Hale Performance build when the BB stroker craze first started taking off. It was a simple 4.15" crank build, stock rods, template ported 906 heads, 750 vac sec Holley, very streetable, and made pretty close to the numbers (508hp but can't remember the TQ #'s) you were after with a little .484 Purple Cam. I remember it ran 11.24 in a 3300 pound car with 4.10's and factory truck torque covertor. The KISS principle was applied and it worked.
Anyways, keep us posted!