I just did a full "crawl through" on my new-to-me, 1979 Venture 25.
It has lots of loose blocks of floatation foam (Styrofoam actually).
The stern area has about 10 or 12 blocks of the stuff. There are several other areas where there is under-deck stowage compartments in the cabin, and in each of there there are 2-5 blocks.
Under the bow, beneath the sleeping area, there's some but I couldn't really check the quantity or size. I'll get back out there today.
Do you want pictures? Are you still on the site? (Noted you have only posted one message back in August).
Let me know if you're still around
Rick Donaldson, NØNJY
It's better to be hated for who you are, than to be loved for who you're not.
Let those winds of change blow over my head,
I'd rather die while I'm living than live while I'm dead - Jimmy Buffet