Thanks fellas. I thought I might get flamed a bit, but the pro's are out tonight.
The hard to remove 2 rooms that the PC was painted I'll sponge off the heavy chalk remains and most likely pull a tight coat of mud. The others, sponge off, pull where needed, spot and seams.
They're all going back to smooth dw. Its not stained but about 35% of the original surface looks like real old dw (built 1965) brown most likely from the age and heat of the attic over the years.
Looks like a good latex primer sealer will do. I was concerned about the remains / chalk creating an adhesion problem with latex primer but I'll clean it up ? Cover Stain would be full proof.
The owner (this is a FC in a good neighborhood) gets in there and works the job too. I just want to give the best input but ultimately its his call. I originally said ob primer for all the right reasons. I'll let you know.
Any other input is appreciated.