When I was writing this chart for my beginning guitar student, I struggled and failed to find an easy way to approximate the intro melody on guitar. Advanced guitarists could probably make up a simple chord-melody arrangement, playing the melody on the 3rd (G) string while letting the 4th (D) string drone. A richer-sounding intro could even be achieved using Drop-D tuning. But if that's over your head, I'd recommend shortening the intro, just playing that D7 for a few measures (not 7--way too tedious) or even playing a more predictable G chord for a couple measures.
Remember, as a guitarist you might be obsessed with things like getting the intro to sound good. But most of the people you're going to play with--family sitting around the campfire, classmates hanging out after school, friends swapping songs over a few beers--could care less about the fancy riffs that serve as intros or interludes to songs. Sure, they sound nice, but what they really want to do is sing along, or hear you sing. So don't sweat the riffs you can't play. And don't interrupt an otherwise great singalong song by laboring through a hard guitar part at half-speed, breaking the song's momentum. Just skip that part until you've got it down.