Yes,possibly coil-anything that would lower the voltage at
the plugs or increase the needed voltage at the plugs like excessive gap(likely) or high resistance wires or slow cranking speed from resistance of cold oil causing the starter to draw increased power lowering the voltage at the coil input and output.
I would verify correct plug gap if not the answer clip a jumper from bat positive to switch side of coil to eliminate possible resistance in the primary wiring and switch.If not the answer-then consider the coil and high voltage wires.Often the coil to dist high voltage wire is overlooked and can really be a killer.
with someone else cranking, allow a plug wire to spark to ground paying attention to how the spark can be made to jump-then do the same with the coil to dist HV wire the spark should be able to jump at least 1/2 inch--don't worry about color that no longer applies with resistance wires and maybe rotor.Then use a known good wire from coil output to ground and compare the spark intensity with what you saw when using the wires.
Note: The length the spark is able to jump to ground is a direct indicator of the coil output voltage--the jumper wire to bat hot post will assure proper power is available on that side of the circuit but the ground side wiring needs to be considered too.
yes the naysayers will say the coil will be damaged by our test calling for max output voltage and not giving a path to ground and that is possible but not likely in our short test and if the coil failed it probably had some failing internal insulation anyway.
If low output is detected and coil is not at fault a voltage drop test with a VOM will probably reveal some inadequate wiring/connections.
please let us know what you find.

Bob Taylor