Grabbing a 302 from an Explorer is a good idea.
Stroking it to 347 with the 302 heads and induction is not such a good idea.
Here's a good article on what's involved in making HP. Look at all of the parts that are "beef up" parts:
https://www.hotrod.com/articles/make-503hp-with-a-350-junkyard-302/
With an explorer motor in good shape, I'd replace all the important hardware with ARP, replace the cam, gaskets and seals then boost the crap out of it with whatever Super Charger floats your boat.