I suspect that "the book" for older aircraft is simply the techniques of the flying syllabus of the day. I suspect that the Cubs "book" probably not be much different from the book "Stick and Rudder" or the military ab initio training syllabus of the day. So its nonsense to say they should be grounded.
As for lowering flaps during takeoff roll, you are asking for trouble along the lines of what happened to the guys mentioned in the report referenced below. It describes resulting accidents as well when either the flaps choose that moment to fail to extend or have simply been forgetten because of workload.
"Being suspicious of such claims in increased takeoff performance, I spoke with an Air Tractor representative who confirmed that not only was this takeoff procedure improper, but the theory behind making such a departure is untrue; the drag created by the wing flaps is negligible during this phase of operation, and will not decrease the takeoff distance by a measurable amount."
http://www.agairupdate.com/aau/artic...apEnglish.html
Flappy, I'm surprised that your manual contains a "demonstrated Maximum Crosswind
limit". Mine simply states "Demonstrated Crosswind Component", and I was taught that this is indeed not a limit, but only what has been demonstrated. If your coordination is very good or you get a lucky gust, you can sometimes do better than whats been demonstrated, but again of course you are being your own test pilot.