SBM strokers can perform well with stock heads, if your not looking for all out HP. We have built many of them, and there are a LOT of guys here that have stock heads on their strokers that will tell you they perform very well.
And even if the goal is big hp, the stock castings have a decent amount of room to get into 500's hp range.
Stock port volumes are in the 155-160 range...and when ported to the 260-285cfm, approach 175-190 cc.
I currently have some 915 J heads at 186cc's and 273-282 cfm @.500-.530 lift which is without a doubt enough to allow a 410cid sb to dip into the 500's HP range. And it will also rev high 6's just fine.