I jack my 164 and 144 on the floor just inside the box
frame but I put a block of wood between the floor and
the jack and then put a jack stand under that same piece
of wood (long piece of 2x4 scrap). I put the wood just
behind the jack support area and just inside the seam of
the box frame so it isn't *exactly* the floor but right
next to it.

I've dropped (let the oil out of the jack) a 122 onto
a jack stand on the floor -- it just dented the floor a
little bit but didn't seem to do much else. This was a
122 with rust holes in the floor too.

Volvos seem to be pretty sturdy...
chris