The earliest model year Ford Windstar I see listed in the LATCH manual is the '95 model. Is it possible his is really a '95 model? I think the '95 models were the first model year in the U.S. for what it's worth.
At any rate, I can post what's listed for the '95 model year and hope it's the same for his van, and the part number information is supposed to be the same for the U.S. and Canada.
The '95 through '98 Windstars have 2 factory equipped second row tether anchors under the bottom of the bench seat or in the rear crossbar of the second row bucket seat supports. The third row can have 2 tether anchors retrofitted for the outboard positions. The part number is YF2Z-15613D74-A and there are 2 drilled holes in the bottom of the seat cushion rear cross member. Ford will pay Ford dealerships for retrofitting the additional tether anchors according to Ford Program R7C.