The floatation standards have changed in the years but I thought that atleast the "swamped floatation" standard would have applied to all V-20s built. Today a V-20 would have to conform to the "level Floatation" standard. My 1972 V -17 had foam in it.
Below is a link to the boatbuilders floatation standards
http://uscgboating.org/safety/boatbu...on_landing.htm