While going through the parts DVD today, I ran across the drawing for the left-side observer window. I called and talked to Bruce in tech support, and he said the cost for the "kit" for this is $285.35 at the time of this writing.

It's one of those things that would be best accomplished during a recover since there are parts that need to be welded in. I think I would dig it, though.

Left rear observer window is only useful for rear seat passengers or perhaps if pilot operates from right seat.
The left seat pilot cannot use it at all.

I concur. This would be for passengers.

Anyone know how much weight this ads if any? Would like to do this during recover but I'm real cautious about adding weight aft.

It is three short pieces of .035 and a piece of plexiglass, maybe ask for a price on steel only?