[RodB]

The capacitor can is the common negative side of the three capacitors inside.

I'm assuming the wire that was attached to 4 is coming from the power transformer center tap and the wire that was attached to 1 goes to the 300 ohm resistor. Those 2 wires connect to the negative side of your new capacitors, all 4 connected together. After you make the connection use an ohmmeter and the schematic to make sure the rest of the circuit is connected. It should be OK because I see wires running away from the 300 ohm resistor.

The parts list shows 91 is a one section electrolytic capacitor of 8mfd for code 125 or 10mfd for code 126.

I see a 4mfd electrolytic attached to the big wirewound resistor #90. In the schematic there is a 1mfd capacitor connected to the resistor. Perhaps this is a replacement either from a service bulletin or a part failure? It doesn't have Philco markings.