It's hard to argue with a 393. 351's are everywhere, I got one complete and running for $200, and it even came with it's own method of transportation via the Bronco it was running in.
UPR 351 intake ~ $300 on ebay not polished.
3.85 crank ~ $200
factory 302 pistons ~ dirt cheap
351 crown vic oil pan ~ $40 - www.car-part.com
solid motor mounts for clearance ~ $40 shipped ebay.
157t 28oz flywheel ~ $100 shipped ebay
28oz balancer ~ $70 shipped ebay
Swap headers ~ $300, or cut/lengthen your downpipes shouldn't cost you more than $50
Miscellanious rebuild stuff ~ $250.
So for give or take $1200 plus what you pay for the engine you've got 393 cubes under the hood, You're going to be hard pressed to beat that price going with a 302 based stroker instead.
If I were for certain that a 331-347 was going to give me the power that I am looking for by just swapping my existing parts over to a Dart block, there would be no question as to should I go 302 based or 351 based. Now if I am going to have to buy different heads and intake for 331-347 to get me what I want, I may as well get a 351 base and buy those same parts for it.
It seems to me the price of going 331 or 347 out of a 302 block is about the same as doing a 351 swap and making a 393 out of it.
If you're talking Dart block the stroked 302 will be more expensive. A Dart block isn't ready to go when you buy it, you also have alot of prep work to pay for at the machine shop prior to building the motor.
on the upside to the factory 351 it's certainly stronger than the factory 302 block. How it compares to the Dart version I can't say. But if I'm not mistaken the Dart 302 block is about as heavy as the factory 351? So it's nice to have those extra cubes for extra power to offset the extra weight.
Like I said before, it just seems to me that it's hard to argue with a 393.