351 stroker kit.

Stroking a 351 to 427 puts much more stress on the engine. They say that the maximum dependable cubic inch 351w stroker is 408. When you stroke the engine to 427 it puts the piston rings real deep in the cylinders which increases wear on the engine b/c of the oiling. It might even cut the cylinder walls too close. There are guys on these forums much more knowledgable about it than I am so they can give a better answer, but I am stroking a 351w to 408 currently. He can make a ton of power just using the 351w without stroking. I'm sure he's planning on keeping that '94 street legal as well, so he's going to have a hard time making a big stroker with tons of power street legal. As far as block stress, cooling problems, and longevity, a stroker motor is really not made for any of these. A stroker motor is made for maximum power. I would really recommend keeping the block stock and upgrading the rest of the components. He can still make tons of power that way.

yeah i wouldn't go any more than 408 either for a street engine but the newer 427 kits on the market are a lot better than the ones from just a few years ago, it would probably be fine but i still wouldn't go more than a 408 stroker kit for a street engine.

these days the materials used in pistons is far superior to what was used in the 60's. that said however, i also would not go larger than the 408 in the 351w block. a 393 or 408 can make nearly as much power as a 427 kit(with in 10-15hp @ peak power), and last much longer.

393 is cheapest way to go...
408 is max way to go and be long term...
427 is just plain maxed out...