The third seat setup on the 700/900/90 wagons seem a wee bit larger; yet not too much. Maybe more depth from rear-facing rear seat to the rear hatch / gate.

The 700/900 is a wider body versus the 145/245/265 Certainly more room for the two front occupants and the three rear seat occupants. Still, though 2+5 seating.

A trip to a salvage yard with a third seat or of you find one for sale may allow you to try it out and measure for space. I believe the third seat in 700/900/90 wagons secures only two occupants. Maybe three? I'd have to look again at one of these.

Check out the 700/900/90 FAQ here:

http://www.brickboard.com/FAQ/700-900/ThirdSeatInstallation/thirdseatinstallation.htm

Shows third seat install in a 700/900/90 that did not have a rear-facing third seat. Looks like the 245 third seat that can support and secure only two occupants.

If you get a 700/900/90, then you have all the wear items diagnosis and replacement unless the prior owner has maintained the vehicle and provides records to the effect.