Ok... another question.?
I would go with the 351 there is no replacement for displacement! However, there a few things you need to keep in mind. First and foremost the 351 has a longer stroke(not larger pistons, both blocks have a 4.000 inch cylinder bore) than a 302 thus making it wider and taller. You have to use intakes made only for a 351w. 289/302, 351 cleveland and 351 modified intakes will NOT fit. Also, to put the 351 in your stang you need a fox body pan for it ford racing, canton, and mildon all make this style pan 302/5.0l oil pans will NOT fit. If you use 83-93 5.0l convertible motor mounts and the right intake/carb set-up you can get away with using the stock hood. Otherwise, you need an aftermarket fiberglass hood raised hood like a 2.5 inch or so cowl induction for example or cut a hole and use scoop. Hoods for your 82 are out there, but are harder to come by than the 83-86 and 87-93 foxbody style hoods. The bellhousing for the 351 and 302 are identical so you don't have worry about that. However if you go with the 351w I wouldn't recommend running a stock t-5, I would go with a c4 automatic or a tremec 5 speed. Then you need to get a set of 351w swap headers, various manufactures make these. Also, if you want to go with a Serpentine belt set-up and you want to go with power steering and air conditioning you'll need to buy swap brackets, I see these on ebay and I believe ford racing might still make them also(not 100% sure on that one though). If you go with a serpentine belt set-up 5.0l pulleys will swap over, and you'll need a reverse rotation water pump. The 351w is a stronger block than the 302. As stated before yes it is heavier, but it can handle more power through it. Also, I would upgrade the front brakes and suspension. Then I would definitely add some sub-frame connectors with either engine you go with. Hope this gives you some of the insight you were looking for. Not matter what set-up you go with good luck with it and have some fun with it when you get it running.