try http://www.carseatdata.org . they have a searchable database where you can enter your car's year, make, and model and which type of seat you're looking for (e.g. rear-facing convertible) and it will show you the info that other users with the same year/make/model have entered - make/model of car seat installed, where it was installed (e.g. second row passenger side, etc.), how easy it was to install and how well it fit.
I also recommend posting your question on the forums at http://www.car-seat.org/ . Many of the regulars there are certified child-passenger safety techs and all the regulars are very helpful and well-informed and can help you find a seat that fits your car, child, and budget.