Cheap V-20 project

I know I'm going back to page one of this post, but sometimes I'm a little slow. Foam under the floor was mention and it seems everone is saying Wellcraft didn't start putting foam under the floor until late '70s - early '80s ish... My boat is a 1971 and this is what I found while removing the rot from the transom



I'm not sure if that's Wellcraft's work or someone's personal handywork, but it appears to go the length of the floor between (but only between the stringers). I'll know for sure once the inner liner is out.