Not all L-450's were supplied with 4 wires. The low inductance models (1.6H, 2.4H) came with two wires.
Splitting these pickups would be pretty pointless as they have several tonal similarities with single coils and the split sound would be considered very thin and weedy by most players. This goes for the L-600, too.
L-609s and L-610s are a different story though. They do not have multi wire options at all because their design is very different from twin coil humbuckers'.