First of all, keep in mind that while 1E and 3E have a lot of points in common, 4E is really its own beast entirely. You can take a 3E stat block and simply trim out the parts you don't need and you get a pretty decent 1E approximation, but in 4E the terminology and power scale is so different that there aren't many elements in common.
I run 1E/3E adventures in the DCC RPG without much conversion at all (other than trimming out the 3E stuff I don't need). In early playtest I used a lot of older DCC modules since we didn't have a real source of official stuff at the time.
Having said all that, an adventure is basically an adventure and clearly the text and plotline don't need to change. What you would want to do for 4E is basically throw out the monsters and redesign them in DCC. Take the "soul" of the monster and recreate it without worrying about if the new one is a true conversion, but instead give it whatever special spark made that monster unique in 4E. For example, if the adventure calls for a dragon throw out the 4E version and grab a 1E dragon instead, or simply make up a dragon using DCC rules. Don't try to fiddle with a 4E monster to somehow make it fit.
Keep in mind that balance isn't as important in the DCC RPG as it is in some other games. If a monster is too easy, throw more of them at the characters next time. If the monster is too tough, characters die or get smart and run away. Don't stress trying to "get it right" but instead have fun with it.
That's my usual plan for conversion.
_________________Marv / FinarvynDCC Minister of Propaganda
; Deputized 6/8/11
DCC RPG playtester 2011, C&C
since 2003, ADRP
Since 1993, OD&D
player since 1975
"The worthy GM never purposely kills players' PCs, He presents opportunities for the rash and unthinking players to do that all on their own."
-- Gary Gygax
"Don't ask me what you need to hit. Just roll the die and I will let you know!"
-- Dave Arneson