1971 slant six 225 no spark or weak spark at plugs?

Bear in mind that points with high resistance, bad/ partially bad condenser, weak coil, poor grounds in the distributor, low voltage to the ignition system can all cause this.

BEST way to test spark is to use a WIRE core coil wire, even a piece of non spark wire, if you can "hang" it out in the open away from metal. "Rig" a spark gap, plug, or buy a gap type ignition tester. When cranking WITH THE KEY it should generate at least 3/8 and usually 1/2" nice snappy blue spark

Clip your multimeter to coil + and ground, and turn key to "run." you should see 6-10v or so. NOT full battery if the points are closed, and you want them closed for this test---but don't leave the key on for long, you can burn the points

Then crank engine using the key, and read meter while cranking. Note that reading, then read battery voltage while cranking. They should be very close to same

Anybody that uses breaker points really should use a dwell meter for several reasons. You can find them used. They will generally check points resistance, voltage to the coil, and of course points dwell.

Find out if points switching is actually working. "New" does not mean "good" parts. After measuring coil voltage, hook meter to coil NEG. Turn key to run. Voltage with points closed should be low, lower the better, perhaps 1/2 volt. Manually open points. Voltage should go to full battery. Manually operate points and see if you can get a spark that way. If not, with points blocked open (light cardboard) short them closed with an alligator clip wire or screwdriver Should get a spark

If you can switch open points, if the voltage checks out, and no spark, I'd try a different condenser, and if no, another coil