before I ran out of money on my mustang, I was considering stroking my 351W. The shop that was going to do it, (eventually it just rebuilt the engine with ported alum. heads, Hedman long tubes mated to a new cross over (x junction) dual exhaust with new flowmasters, forged pistons and rods, new custom grind cam, holly double pumper carb, etc, at a 10:1 cr) advised me that 396 was as far as they would recommend stroking a 351W, with 408 definitley pushing the envelope, and anything beyond that being just too much for a small block to handle and not court trouble in the future. If you want a 427, then you should start with a 390 bb. I have no personal knowlege to back up what I am saying. Rather, I am simply passing on what I was told by pro builders. As for me, I am told that I should expect about 450 hp at the fly. That is plenty enough for a street ride.
JS