I,d check with the engine builder to see if it had an internally balanced crank installed when it had the 408 crank installed.My 408 is internally balanced.
And true to the previous poster about convertor technology, I am running a 3500 stall 10 inch convertor on the street behind my small block stroker, and I love it. When in drive at a stoplight idling, it will try to pull the car forward slightly, nice and tight, and flashes perfectly. And my cam is very similar to yours; I am running a 241 / 247, 545 lift on a 110 centerline.