2wd to 4wd conversion on a 77 Ford F-150?

So I'm getting an old 77 ford from my buddy for about $700. I planned to do a restoration, but I put some thought and might throw abit of some modifications to it because since it's stock height, carburated and 2WD, I'm automatically gonna have trouble during the winter. My friends and I have been talking about a 4wd conversion, I've seen people do it with Leaf springs. And I've read that they fabricated the frame to make it 4wd capable. But I don't have a welder nor the experience of welding so I really don't wanna mess anything up. So my main question is, is it possible to do the swap for the 2wd to 4wd without cutting into the frame? It's a 77 ford f150 but what I don't know is if they changed up the frames of the 2wd and 4wd. It sounds a little confusing because it's alittle confusing for myself. But it'd be great If I know what I should do. Thanks.

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