I'd use the stats AS-IS. I do it all the time. Though I havent' done so with 4e stuff, the way those adventures are written, it might "feel" funny with all the compartmentalized encounters, but it could work.
The STATS between editions have become tropes, and pretty much work the same no matter what. Hitpoints are the same. AC is the same. Saves can be weird, but they're Defenses in 4e, saves in 3e, but plain old ability modifiers in 2e and earlier. It should be easy enough to convert on the fly.
Every edition's power curve increases as the edition increases. But I don't think it's a big deal that a 0e orc is weaker than a 3e orc. Just imagine that they're different orcs. It's not a big deal.
DCC RPG doesn't focus on Encounter Levels or Challenge Levels. But DCC RPG characters are so dynamically broader in power, it'd be interesting to see what happen. I don't want to get into the philosophy of encounter design between editions, but in later editions there are assumptions that encounters are "balanced", while in early editions those assumptions didn't exist, and you really had to be a good GM and leave enough clues or pull some punches early, to give the adventures an idea how powerful the encounter was going to be, so they can make an educated decision to flee or fight. DCC RPG emphasizes that style of play, which a lot of modern gamers aren't used to.
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