I'd fix the one you have. Even if you have the money for that newer truck, that isn't what you need. Because you might end up with no money and have to fix that one. I would highly suggest fixing yours so you can learn a little bit by experience. That is the only way I learned anything about cars is by doing it myself. Nobody in my family is mechanically inclined so I had no one to back me up on what I was doing. But man, I look back and I was pretty successful with my engine swaps and current rebuild. Just throw a 302 from the junkyard back in it if you have to. It's not the end of the world right? Just some labor. And I know it's a little more work to put in that 351, but someday after you do your 302 motor swap, it'll be that motor instead. Wish you the best, keep your money.