if it is a 30.06 the magazine box should be of standard lenght and if it is a totally removable floorplate which is what it must have been for you to loose it, than it is most definetly is a standard lenght floorplate many JPs "US models" were built on oberndorf actions with inside trigger guard button release
whatever the case you will have to gunsmith a new lever ,NECG.COM may have the parts to construct this ,post a pic ....paul