NOT SINCE Kiss wiped off its makeup and Elvis loosened his (tummy-tucking) cinch belt has the world witnessed an event like "Unwigged and Unplugged," the touring show starring Michael McKean, Christopher Guest and Harry Shearer.

You know these guys better as (respectively) David St. Hubbins, Nigel Tufnel and Derek Smalls, the dim-witted heavy-metal rockers from the 1984 cult comedy classic "This Is Spinal Tap." Or as self-absorbed and cliche-riddled folk music revivalists the Folkmen from another great mockumentary, 2003's "A Mighty Wind."

This time around, playing the Keswick on Thursday, these longtime friends and collaborators are doing normally "cranked to 11" "Tap" tunes like "Big Bottom" and "Listen to the Flower People," and quasi-folk parodies like "Old Joe's Place" and "Blood on the Coal" as, well, themselves.

Sans wigs and fake accents.

And in a stripped-down, acoustic fashion that underscores (say reviewers) just how funny their lyrics are and how well these dudes do play. Of course you'll be smiling, even before the lights go out. But this time the idea is to laugh with the guys, not at them, as these improvisation-minded performers let the spirit move them.

For sure, they'll be interspersing the ditties with videos (some made by fans) and do a dramatic reading of an NBC network edict on how "Spinal Tap" had to be edited for television.

They'll also take questions from the audience and maybe allude in story and song to some of their many other projects alone and together: Guest as a screenwriter, director, actor and member of the meditative-instrumental Beyman Brothers band; McKean, lately, as a Broadway star; and Shearer as a core vocal impressionist of "The Simpsons" and host/creator of the syndicated public radio hour "Le Show."

Earlier this week, I got on the line with Guest to talk about how this tour came together and other such rubbish.

Q: This concert show was originally billed as "Unwigged, Unplugged and Undead." Did someone think that was a bit much, even for you guys?

A: It may have been. I don't remember why it got changed. The origin of all this was at the Museum of Modern Art three or four years ago, where there was a retrospective of my film work ["Waiting For Guffman," "Best in Show," "The Big Picture," et al]. When asked what I wanted, I said I'd like to do some music, too. So the three of us got together to perform acoustically, and had so much fun, we said, "We've got to do this again."

We originally thought about doing a full-blown "Tap" tour this year to mark the 25th anniversary of the film's release. But that would have been a very big deal in terms of show production, requiring a lot of effects, two 18-wheelers full of equipment, a tour bus.

To be honest, we couldn't get that together. But we will do a couple of "Tap" shows in Britain, at Wembley Arena and the Glastonbury Festival.

Q: I'm presuming you've had contact over the years with heavy metal and folk musicians. Do they see the humor in your satires?

A: Folk people enjoy "A Mighty Wind." They got it. There are differing camps in the heavy-metal area, some who are, I think, disturbed by how close that film ["Spinal Tap"] is to the truth. Much of it is based on a tour I did with McKean in '79 as Lenny and the Squigtones. It started out well, then we lost record company support [and] everything fell apart.

Characters like promotion person Bobbi Fleckman [hilariously portrayed by Fran Drescher] were based on people on that tour. So when a musician sees that and it's too close to the truth, it won't be funny. Those who do find it funny, they point and say, "I know that person," but it's never them.

Q: Is it true you guys never made a penny off "This is Spinal Tap"? But on the other hand, didn't it open a lot of doors for you?

A: In the movie business, it's quite a chore to receive what you are owed. To put it simply, in this case, we got zero. As far as being a launching pad, it's important to point out that the four of us involved - and I'm including director Rob Reiner - were not finding any support for this project. No one would make it. People didn't get it, didn't think it was funny. Then Norman Lear said, "Here's the money, go make your movie." Without him, it just wouldn't have happened.

Then when Rob formed Castle Pictures, I could go to him and say, "I've got an idea for a picture," and he'd give me the green light, 100 percent control. The only guy who would. That doesn't exist in a typical Hollywood scenario.

Q: Michael's wife, Annette O'Toole, and Harry's wife, Judith Owen, have been popping up on this tour to perform. So where's your wife Jamie [Lee Curtis]? Is she tone-deaf? And how come she never shows up in the acting ensemble of your films?

A: Judith comes and goes. Sometimes she has other shows. Annette is definitely with us. We have other people lined up as guests in Nashville, New York, some other places where we know people. Jamie's at home with our 13-year-old son.

Our daughter's in college now. We've been married 25 years and from day one, we made a point to say we'll keep our working life separate. I can't speak for other people, but it really makes our home life just that.

Q: Rumor has it that you never look again at the movies you've made. True? And what can you tell me about your participation in the "Night at the Museum: Battle at the Smithsonian" sequel coming out in a couple of weeks?

A: The process of making our movies [often involving the writing participation of Eugene Levy] is different than most. We sketch out what we want to have happen in a scene, then let the actors improvise. We have a short, 28-day shooting schedule. Then I'm in the editing room for an entire year, much longer than normal. So when I'm done with a movie, I'm really done with it.

I'm playing Ivan the Terrible in the new "Night at the Museum." It was a good stretch as an actor, and I had a lot of fun working with guys like Hank Azaria and Ben Stiller.

They're having a big premiere in Washington and were ready to helicopter me in from Baltimore, where we're playing an Unwigged show the same night. But logistically, there was no way I could do both. These guys and this gig come first. *

Keswick Theatre, Easton Road and Keswick Avenue, Glenside, 8 p.m. Thursday, $47.50-$62.50, 215-572-7650, www.keswicktheatre.com.