They're notoriously picky about placement - separation, toe in, tilt back, distance from walls and corners. Experimentation IS required as a couple inches can make a big difference. Don't raise them very far off the floor.
Future??? recap, new horn diaphragms, and a sub. While they're opened up, some seal the seams, some add bracing.
The serial numbers should be stamped on the back edge and will lead you to the manufacturing date.