The benefit of going with a stock motor over your setup is pretty much nothing. You would gain torque, lose horsepower, and lose mileage.
My brother and I are looking at putting a built 351 I have in his SN right now. There is a lot of research involved.
Its hard to determine which are roller blocks unless they are torn down, and some roller blocks still have flat tappets in them. Regardless, a solid flat tappet will produce almost the same results at lower cost. Great comparison on this in hot rod a couple months ago.
IF you could get an all stock 351 out of a 351 lightning or cobra that would be different - but that would likely cost more than its worth.