Be prepared and safe with an Interlock kit for your existing panel
If you have an FPE panel you could be out of luck. I looked high and low. You can change the guts to a newer brand. You will have trouble with your insurance comp. anyway. "they don't like FPE" not only are the breakers not accurate,  the panel dimensions are too small also. 

GE interlocks

GE 150 - 225 Amp PowerMark Distribution Gold Load Center Generator Interlock Kit

GE-200HDA GE Generator Interlock  for Verticle Main  150 or 200 amp         

GE-100A  GE Generator Interlock Kit 100 or 125 amp panels

L14-30 Generator Power Cord 4 Wire 10 Gauge 125/250v 30 Amp 20 Feet

PB30 30-Amp NEMA 3R Power Inlet Box for Generators Up to 7,500 Running Watts

Auto Transfer Switch - 30 Amp

GE-200VA GE General Electric Generator Interlock Kit for Vertical Main 150 or 200 amp breaker

ge 200,.jpg

GE-1 Generator Interlock Kit for General Electric Breaker Panel

50 ft  6/3 - 50 AMP

30 Amp Generator Cord, 10 Gauge Heavy Duty L14-30

Adapts a 4-prong 30 AMP L14-30 receptacle to two -15 receptacles

Power Inlet Box, 50-Amp for Generators Up to 12,500 Running Watts