[mr48chev]

A spark at the points shows that you indeed have power going thought the primary circuit of the coil to the points.
Thing is, a bright white spark there is a bad thing. You want the points to open and close with no sparking as they are the switch that turns the primary winding in the coil on and off so it builds up a magnetic field and then the magnetic field collapses and creates the high voltage in the secondary of the coil that is the spark that goes to the plugs.

With the rubbing block of the points on the tip of one of the distributor cams (that's that little plastic looking block on the arm of the points against one of the points on the six sided piece on the distributor shaft) you want about .016 gap between the points. Then the points can open and close and make the coil work.

Since the later engine was installed did they convert to 12 volts and is there a ballast resistor? If you have a resistor you also have to have a resistor bypass wire from the solenoid to the coil so that you get a full 12 volts at the coil when cranking.
Also if someone did a switch change there are a few ignition switches that do not put power to the coil when they are in start position relying on the bypass wire to do that. On those if everything is perfect in the universe the truck will actually start after you let off the key when you are cranking it and it goes back to the on position.