I've seen a bunch of swaps done but that isnt one of them. It usually comes down to why? The 4.2 v6 just isnt that impressive and it was never offered in a RBV platform so it's a full custom swap. The 5.0 v8 swaps into a ranger with factory parts so most people just do that. Not discouraging anyone from being weird. Just being logical.
A 4.2 makes a lot less power than a 302 and I believe it's wider so it would be a more difficult swap, if you're doing it just because you want to, then go for it. I once saw a Pinto with a flathead in it, it was cool but he probably had less power than the original 2.3.