Peter,

My FB 360 from '98 has no reinforcing in the floor honeycomb area.  I
use a 4" square block with felt on top of my jack stand.  It does fine
jacking under the forward edge of the close out rib under the center
spar section.

I suppose if you wanted to use that preset piece of phenolic I would be
inclined to reinforce it to the rib with 6 or more BID.  One hesitancy
would be that it is apparently about 6" aft of where I jack my plane.
That is, it would seem to require substantially more tail weight to get
to nose to come up (hold down the tail).  I have the long mount.

Probably a better solution would be to core out a little two inch square
area under your spar skin area and put in a new phenolic block.   This
then could have a little hole for jack alignment.

Larry