Hi porschefan,
Didn't you get other errors apart from the ones you mention?
I'm running CUP too and I have imported those missions. I've had to make quite a bit of tweaking in the mis files to get rid of the errors. Mine were about missing planes or incorrect class names in the mis files (when imported in CUP of course). I was getting clear error messages when loading the briefings (at least for the A-26/B-26 issue).
First, there's no A-26 in CUP. Only the B-26. I've had to change the name of the class in the impacted mission mis files.
Second, several J-87 class names are different in CUP. In CUP Ju-87 G1, D5, etc. have a "j" at the end of their class names.
Finally, for the B-26, I found that one of the proposed loads (don't remember the mission) with rockets and napalm does not exist in CUP. I assume that is because we get the B-26 which is the bomber version of that plane, and it's not really intended to get attack, low-level bombing loads. Personnally, I've replaced it with a 16x300lbs load.
With these fixes, the missions seemed to be OK. I have had no time to really try them though.