1984 Ford Ranger "britax" Questions

Fitted my britax duo isofix seat into our discovery 57 plate for there to be a large gap underneath the seat and carseat which i feel isnt safe? Britax duo plus isofix carseat. What is a "57 Plate"?

...Do you have any ideas? My Gerber infant seat worked fine and firedepartment said they checked good. Britax Rock-a-tot seat works fine rear-facing using the alternative routing and Britax First Class ...

...know what convertible carseat to use, as my son is outgrowing the Graco SnugRide. I really want the Britax Marathon, but I think it may be too big for the FX's small backseat. I don't want to have to ...

...have a 1994 Jeep Wrangler. Where is the safest place to install a car seat? Front? Back? We have a Britax five point upright convertable car seat. rear seat facing backwards. Safest place to install ...