There's been a long-standing issue that PDC cannot be refit. AFAIK it hasn't been fixed.
That being said, a construction brigade has industrial output equivalent to a single factor. So a they can do anything a factory can do (although they'll do it very slowly, since it will take a LOT of CB's to get a decent output).
I suspect that what you heard was about prefab PDC. You build it on a planet with a lot of output as a prefab, then ship the parts (and some extra minerals) to a planet with low output, where it can be assembled at 1/10th the cost.
John