ORIGINAL: RC-FIEND
I have built kits that were 40+years old with no problem, and have some excelent 50 year old balsa among my supplies.
I have to say that incredible ! do you still have them ? I would love to see what models you are talking about from 40 years ago. As far as balsa goes if it ain't fresh I would not attempt to build with the stuff . The choice is yours.
Actually I have some kits that are even older. Examples from the late '30s include a Sailplane, a Zipper and a Playboy. I will save these as collectables, though the quality of the wood is fine. Why would you have reservations about old balsa? Like other woods as long is it is kept dry, strored flat and protected from insects the shelf life should be indefinite. Bear in mind too that the longer wood cures the less prone it is to warp.
BTW I have several CL models that I built in the late 50s that while in need of recovering (silk and dope) are otherwise quite flyable.
jess