I was out till dark last night bear hunting. When I got home, I should have
gone to bed Instead of trying to answer your question. I will try to set
things straight.

I called that partition a firewall. It is not what is commonly known as a
firewall.

In my hurry to finish my letter, I failed to mention that you would need a
leg for the right front corner of the bed by the sliding door. Also since
you probably have paneling ( if that is what it is called) It would be much
simpler to use two front legs and forget the side rails. These legs can be
made of 2x2 lumber. I cut mine to the proper length and bored a 3/8" hole in
the top end and inserted a 3/8" steel rod. A 3/8" hole was bored through the
corner of the plywood to accept the leg.

I just now went out to check the ribbed panel in the back. Boy!! What a
change, unless I forgot. You probably would have to contour the edges of the
plywood to make a close fit. If these attachment points are made strong and
tight enough, there will be no wobble on the front legs.

A bed made this way will come out easily and the only parts left in the van
will be those 2 strips on the back wall.

And Hey!! My Syncro is an '87 not an '86.    Woe is me.

Bob

P.S.  I have everything right this time---that is --till after I click the
"send" button :-)