As a former surf guitarist, I hereby confirm that the rumors are true: heavy-trad instrumental surf rock sounds a bit like heavy metal minus the distortion—but with a lot of soaking-wet spring reverb thrown in.
Take this recent video by the Paranormal Guitar Channel, "Metal Without Distortion, aka Surf Music from Hell."
In the clip, which has already wracked up more than a million views (and an unusually high number of "thumbs down"), the guitarist—let's call him "Mr. Paranormal"—plays tunes by Slayer, Pantera, Death, Cannibal Corpse, Megadeth and Metallica, all without distortion but with a touch of (what sounds like) digital reverb. And yeah, it does sound like surf music from hell and/or purgatory ... or not very good surf music. Be sure to check out the clip below.
If you're interested in some worthwhile surf covers of classic metal tunes, check out Big 4 Beach Blanket Bingo (2014) by Killjoy & The Cutthroats. You can hear one of their songs—a Metallica cover called "For Whom the Beach Calls"—below (bottom video).
And if you're still on the hunt for some great modern surf guitar music, go listen to some Slacktone and be sure to check out "10 Instrumental Surf Rock Songs You Need to Hear Now."