John Bush would be lying if he said he wasn’t at least somewhat leery about suddenly having to share lead vocals with original Anthrax member Joey Belladonna.

But he’s willing to give it a fair shot.

Shortly after Anthrax signed a multimillion-dollar deal with Elektra, Belladonna left in February 1992 after 11 years with the pioneering thrash-metal group. Bush, formerly of Armored Saint, was named his replacement four months later.

Bush has held his own since his debut on the 1993 album “Sound of White Noise,” the group’s sixth consecutive gold-seller. The band also contributed tracks for the Arnold Schwarzenegger film soundtrack “The Last Action Hero” and the Kiss tribute album “Kiss My Ass” and appeared on an episode of the NBC series “Newsradio.”

Then one day, someone at Anthrax’s new label, Beyond Music, suggested the New York rockers – Bush, guitarist Scott Ian, bassist Frank Bello and drummer Charlie Benante – combine the past with the present on their next LP, “Return of the Killer A’s (The Best of Anthrax).” The album, released Nov. 23, features Bush and Belladonna teaming for a cover version of the Temptations’ “Ball of Confusion.” They’re also sharing the stage, Belladonna singing the old material and Bush the newer ones, on an Anthrax tour.

Bush admits the concept caught him off guard.

“At the time, it was something I had to sit back and evaluate to see how I was feeling about it, which was pretty normal,” Bush said recently. “It came up as an idea that there’d be a tour based on the record, because there’s two different eras on there. Then somebody from the record label suggested putting us all together for the record.

“I’m embracing it now; I don’t have a problem with it at all. I think it’s unusual. Anthrax’s never been a band that does things conventionally. I’m sure there will be times when my ego will be tested, and I’m sure it’s true for (Belladonna), but you know, maybe it’s a good idea. If there’s any competition, it’ll probably just mean a better performance.”

Pairing with Belladonna for an aural assault on “Ball of Confusion” was remarkably easy, Bush says.

“I just met him a couple of times in the past,” Bush said, “but we did this (‘Ball of Confusion’) together and nobody was there besides us. Scott was there for like five minutes and took off. The jell came together pretty quick. We did the song, for the most part, pretty live. We had two mikes in the room; we just sang it and it came together rather quick.

“It’s the kind of thing where you don’t have to act like you’re the best of buds or put on some superficial overtone, like, ‘Hey, my bro.’ Just do it as it is, let the relationship develop; if it develops, cool, and if not, that’s fine too. What happened with him and Anthrax had nothing to do with me. Joey did some awesome things with Anthrax, but I also think they were ready to move on into a different direction and that’s how I came into play. People are always going to compare us, and that’s fine, as long as they’re talking about the band.”

In addition to “Ball of Confusion,” the 16-track “Return of the Killer A’s” contains “Bring the Noise,” the group’s 1991 collaboration with Public Enemy’s Chuck D. and Flava Flav, previously unreleased remixes by Ministry’s Al Jourgensen of “Pottersfield” and “Hy Pro Glo,” and such fan favorites as “I’m the Man,” “Got the Time” and “Indians.”

Bush sees it as an overview of Anthrax’s two eras of history and music.

“I just think there’s a lot of great songs that have gone unnoticed in my particular era with the band,” he said. “The songs help each other out; for instance, new Anthrax fans can go back and discover old Anthrax songs and people who maybe haven’t bought the last two records will buy this one and get turned on by the new stuff. It helps the band as a whole. It shows that the band has written a lot of great songs over the years.”

Is the Bush-Belladonna pairing a one-time thing? Even Bush isn’t sure.

“What happens from here, I don’t know,” he said. “The plan is to do the tour here in the states. I think we’re going to go to Japan, where the band has always done well. If it were up to me, we’d also go to Europe.”

No matter what, there’s always something there to remind Bush that things could be worse.

“At the end of the day, I try to keep in mind I’m in a band,” he said. “I’m still rocking out, making music. People envy this career that I have, so how am I going to sit there and bitch? That’s how I keep myself in check.”

BWF (before we forget): The Anthrax album discography – “Fistful of Metal” (Megaforce, 1984); “Spreading the Disease” (Island, 1985); “Among the Living” (1987); “I’m the Man” (1987); “State of Euphoria” (1988); “Persistence of Time” (1990); “Attack of the Killer B’s” (1991); “Sound of White Noise” (Elektra, 1993); “Live: The Island Years” (Island, 1994); “Stomp 442” (1995); “Volume 8: The Threat Is Real” (Ignition, 1998); “Return of the Killer A’s (The Best of Anthrax)” (Beyond, 1999).