I wouldn't be at all surprised if lead paint was used. I was painting houses in Santa Monica California when my 1974 WS 32 "Phantom" was being built. As I recall it, lead based paint was still legal in California at that time.
More importantly, be aware asbestos fillers were mixed with resin (the way micro balloons are now), perhaps liberally, in making putty used in the construction of the WS 32. you could Learn more about that by searching for the word "asbestos" in this forum.
By all means, wear a Tyvek full body suit and a respirator before you start sanding.